JP7653843B2 - Semiconductor integrated circuit, microphone and writing system - Google Patents

Description

Embodiments of this specification relate to semiconductor integrated circuits, microphones, and writing systems.

Conventionally, microphones are known as devices in which a programmable semiconductor integrated circuit is implemented inside a housing that contains a microphone transducer. For example, the gain of the microphone transducer can be fine-tuned by programming the semiconductor integrated circuit.

U.S. Pat. No. 9,161,112

Some of these microphones are equipped with a dedicated terminal for externally programming the semiconductor integrated circuit mounted inside the housing. However, providing a dedicated terminal reduces the freedom of housing design.

The object of the present invention is to provide a semiconductor integrated circuit, a microphone, and a writing system that can be programmed without providing a dedicated terminal.

In order to solve the above-mentioned problems and achieve the object, a semiconductor integrated circuit according to an embodiment includes a transducer bias circuit, a microphone amplifier, a current detection circuit, and a control circuit. The transducer bias circuit applies a voltage to the microphone transducer. The microphone amplifier amplifies a signal from the microphone transducer and supplies the amplified signal to an output terminal. The current detection circuit is connected between the microphone amplifier and the output terminal and detects a current from the output terminal. The control circuit transitions the output terminal to a high impedance state by controlling the microphone amplifier in response to the current signal from the output terminal, and starts a program operation for setting the transducer bias circuit and the microphone amplifier based on a program signal input from the output terminal.

The present invention makes it possible to program a semiconductor integrated circuit without providing a dedicated terminal.

FIG. 1 is a diagram showing an example of the configuration of a microphone in which a semiconductor integrated circuit according to the first embodiment is mounted. FIG. 2 is a diagram showing an example of the configuration of a microphone amplifier and a current detection circuit in the semiconductor integrated circuit of FIG. FIG. 3 is a diagram showing an example of the configuration of a control circuit in the semiconductor integrated circuit of FIG. FIG. 4 is a diagram showing an example of the configuration of a program start detection circuit in the control circuit of FIG. FIG. 5 is a diagram showing an example of the configuration of a writing system that programs the semiconductor integrated circuit provided in the microphone according to the first embodiment. FIG. 6 is a diagram showing an example of signal waveforms related to programming of the semiconductor integrated circuit according to the first embodiment. FIG. 7 is a diagram showing an example of the configuration of a control circuit in a semiconductor integrated circuit according to the second embodiment. FIG. 8 is a diagram showing an example of the configuration of a counter circuit in the control circuit of FIG. FIG. 9 is a diagram showing an example of signal waveforms related to programming of the semiconductor integrated circuit according to the second embodiment.

Below, embodiments of a semiconductor integrated circuit, a microphone, and a writing system will be described in detail with reference to the drawings. In the following embodiments, parts with the same reference numerals perform similar operations, and duplicated descriptions will be omitted as appropriate. In the following embodiments, "connection" means "electrical connection."

Fig. 1 is a diagram showing an example of the configuration of a microphone 1 in which a semiconductor integrated circuit 2 according to the first embodiment is implemented. As shown in Fig. 1, the microphone 1 has a semiconductor integrated circuit 2 and a microphone transducer 5. The semiconductor integrated circuit 2 and the microphone transducer 5 are mounted in a housing (casing) of the microphone 1. In other words, the microphone 1 is a sound collection device in which a programmable semiconductor integrated circuit 2 is mounted in a housing in which the microphone transducer 5 is mounted. For example, in the microphone 1, the gain of the microphone transducer 5 can be finely adjusted by programming the semiconductor integrated circuit 2. The housing of the microphone 1 is provided with a power supply terminal 17, an output terminal 18, and a ground terminal 19.

The semiconductor integrated circuit 2 is an externally programmable semiconductor integrated circuit. The semiconductor integrated circuit 2 is provided with a microphone signal input terminal 3, a microphone bias terminal 4, a power supply terminal 14, an output terminal 15, and a ground terminal 16. The microphone signal input terminal 3 and the microphone bias terminal 4 of the semiconductor integrated circuit 2 are each connected to a microphone transducer 5. The power supply terminal 14, the output terminal 15, and the ground terminal 16 of the semiconductor integrated circuit 2 are each connected to a power supply terminal 17, an output terminal 18, and a ground terminal 19 of the housing of the microphone 1, respectively.

The semiconductor integrated circuit 2 outputs a voltage for adjusting the gain of the microphone transducer 5 from the microphone bias terminal 4. The microphone transducer 5 is a device configured to convert sound into an electrical signal. The microphone transducer 5 is configured to output an electrical signal with a sensitivity according to the voltage supplied from the microphone bias terminal 4. The electrical signal (microphone signal) from the microphone transducer 5 is input to the semiconductor integrated circuit 2 from the microphone signal input terminal 3.

As shown in FIG. 1, the semiconductor integrated circuit 2 has a microphone amplifier 6, a current detection circuit 7, a transducer bias circuit 8, a control circuit 10, a pull-down switch transistor 11, and a pull-down resistor 12.

The microphone amplifier 6 is connected to the microphone signal input terminal 3 and the current detection circuit 7. The microphone amplifier 6 amplifies the electrical signal from the microphone signal input terminal 3. The microphone amplifier 6 supplies the amplified electrical signal to the current detection circuit 7. The current detection circuit 7 passes through the electrical signal from the microphone amplifier 6 to the output terminal 15. In other words, the microphone amplifier 6 is configured to amplify the signal from the microphone transducer 5 and supply the amplified signal to the output terminal 15. Here, the microphone amplifier 6 is configured so that the gain can be adjusted by the program of the semiconductor integrated circuit 2.

The current detection circuit 7 is connected to the program start detection circuit 303 (see FIG. 3) of the control circuit 10, the oscillation circuit 307 (see FIG. 3) of the control circuit 10, and the output terminal 15. The current detection circuit 7 is configured to detect the current applied to the output terminal 15. In other words, the current detection circuit 7 is connected between the microphone amplifier 6 and the output terminal 15, and is configured to detect the current from the output terminal 15.

Figure 2 is a diagram showing an example of the configuration of the microphone amplifier 6 and current detection circuit 7 in the semiconductor integrated circuit 2 of Figure 1.

As shown in FIG. 2, the microphone amplifier 6 is provided with a microphone signal input terminal 203 and an amplifier operation control terminal 210. As shown in FIG. 2, the microphone amplifier 6 also has a high-side output transistor 201, a feedback circuit 202, a microphone amplifier 204, and a low-side output transistor 205.

In the example shown in FIG. 2, the high-side output transistor 201 is a PMOS transistor. The source of the high-side output transistor 201 is connected to the power supply terminal 14. The drain of the high-side output transistor 201 is connected to the drain of the low-side output transistor 205.

The feedback circuit 202 is connected between the non-inverting input terminal (+) of the microphone amplifier 204 and the output terminal 15.

The inverting input terminal (-) of the microphone amplifier 204 is connected to the microphone signal input terminal 203. The microphone signal input terminal 203 is connected to the microphone signal input terminal 3. The control terminal of the microphone amplifier 204 is connected to the amplifier operation control terminal 210. The amplifier operation control terminal 210 is connected to the control circuit 10 via the set value signal node 9. One of the pair of output terminals of the microphone amplifier 204 is connected to the gate of the high-side output transistor 201. The other of the pair of output terminals of the microphone amplifier 204 is connected to the gates of the low-side output transistor 205 and the current mirror transistor 206.

In the example shown in FIG. 2, the low-side output transistor 205 is an NMOS transistor. The source of the low-side output transistor 205 is connected to the ground potential.

The drains of the high-side output transistor 201 and the low-side output transistor 205 are connected to the feedback circuit 202 and the output terminal 15.

As shown in FIG. 2, the current detection circuit 7 has a current mirror transistor 206, a reference current source 207, and an inversion circuit 209.

In the example shown in FIG. 2, the current mirror transistor 206 is an NMOS transistor. The source of the current mirror transistor 206 is connected to the ground potential. The drain of the current mirror transistor 206 is connected to the output terminal of the reference current source 207.

The input terminal of the reference current source 207 is connected to the power supply terminal 14.

The input node 208 of the inverting circuit 209 is connected to the drain of the current mirror transistor 206 and the output terminal of the reference current source 207. The output terminal of the inverting circuit 209 is connected to the control circuit 10. As described below, when the current detection circuit 7 detects the program mode, it outputs a current detection signal 13 from the output terminal of the inverting circuit 209 to the program start detection circuit 303 and the oscillation circuit 307 of the control circuit 10.

The transducer bias circuit 8 is connected to the microphone bias terminal 4. The transducer bias circuit 8 is configured to be able to adjust the output voltage by a program in the semiconductor integrated circuit 2. The output voltage of the transducer bias circuit 8 is a voltage for adjusting the sensitivity of the microphone transducer 5. In other words, the transducer bias circuit 8 is configured to apply a voltage to the microphone transducer 5.

The control circuit 10 has a ROM (Read Only Memory) for storing setting values, a decoder, and the like. The control circuit 10 controls the operation of the microphone amplifier 6 and the transducer bias circuit 8 in response to the current detection signal 13 from the current detection circuit 7. For example, the control circuit 10 sets (programs) the gain of the microphone amplifier 6 in response to the current detection signal 13 from the current detection circuit 7. Specifically, the program circuit 308 (see FIG. 3) of the control circuit 10 supplies a setting signal for adjusting the gain to the microphone amplifier 6. The control circuit 10 also sets (programs) the output voltage of the transducer bias circuit 8 in response to the current detection signal 13 from the current detection circuit 7. Specifically, the program circuit 308 of the control circuit 10 supplies a setting signal for adjusting the output voltage to the transducer bias circuit 8.

FIG. 3 is a diagram showing an example of the configuration of a control circuit 10a in the semiconductor integrated circuit 2 of FIG. 1. The control circuit 10a is an example of the control circuit 10.

As shown in FIG. 3, the control circuit 10a has an inversion circuit 302, a program start detection circuit 303, an oscillation circuit 307, and a program circuit 308.

The output terminal of the inversion circuit 302 is connected to the amplifier operation control terminal 210 of the microphone amplifier 6. The inversion circuit 302 transitions the signal supplied to the amplifier operation control terminal 210 to a low level in response to the program enable signal 304 from the program start detection circuit 303. This causes the output terminal 15 to be controlled to a high impedance.

The program start detection circuit 303 is connected to the input terminal of the inversion circuit 302, the oscillation circuit 307, and the program circuit 308. The program start detection circuit 303 generates an oscillation enable signal 306 in response to the current detection signal 13 from the current detection circuit 7, and supplies it to the oscillation circuit 307. In addition, when the program start detection circuit 303 detects that the current detection signal 13 contains a specific type (waveform), it supplies a program enable signal 304 to the input terminal of the inversion circuit 302, the oscillation circuit 307, and the program circuit 308.

Figure 4 is a diagram showing an example of the configuration of the program start detection circuit 303 in the control circuit 10a of Figure 3. As shown in Figure 4, the program start detection circuit 303 has flip-flop circuits 401, 402, 403, and 404, a logical product circuit (AND logic circuit) 405, and inversion circuits 406 and 407.

The reset terminals RST of the flip-flop circuits 401, 402, 403, and 404 are each connected to the oscillator circuit 307 and receive the timeout signal 305 from the oscillator circuit 307. The clock input terminals CK of the flip-flop circuits 401 and 402 are each connected to the output terminal of the inversion circuit 209 of the current detection circuit 7 and receive the current detection signal 13 from the current detection circuit 7. A high-level signal H is input to the input terminals D of the flip-flop circuits 402 and 404.

The flip-flop circuits 401 and 403 form a counter. Specifically, the input terminal of the inversion circuit 406 is connected to the output terminal Q of the flip-flop circuit 401. The output terminal Q of the flip-flop circuit 401 is further connected to the clock input terminal CK of the flip-flop circuit 403. The output terminal of the inversion circuit 406 is connected to the input terminal D of the flip-flop circuit 401. The input terminal of the inversion circuit 407 is connected to the output terminal Q of the flip-flop circuit 403. The output terminal of the inversion circuit 407 is connected to the input terminal D of the flip-flop circuit 403. In addition, a pair of input terminals of the AND circuit 405 are connected to the output terminals Q of the flip-flop circuits 401 and 403, respectively. The output terminal of the AND circuit 405 is connected to the clock input terminal CK of the flip-flop circuit 404.

The output terminal Q of the flip-flop circuit 402 is connected to the oscillation circuit 307 and supplies the oscillation enable signal 306 to the oscillation circuit 307. The output terminal Q of the flip-flop circuit 404 is connected to the input terminal of the inversion circuit 302, the oscillation circuit 307, and the program circuit 308 and supplies the program enable signal 304 to the input terminal of the inversion circuit 302, the oscillation circuit 307, and the program circuit 308.

The oscillation circuit 307 starts oscillating in response to the oscillation enable signal 306 from the program start detection circuit 303. If the current detection signal 13 from the current detection circuit 7 is not applied for a certain period of time, the oscillation circuit 307 supplies a timeout signal 305 to the program start detection circuit 303 to stop program detection.

The program circuit 308 is connected to the microphone amplifier 6 and the transducer bias circuit 8 via the set value signal node 9. The program circuit 308 is also connected to the output terminal 15. The program circuit 308 is enabled in response to a program enable signal 304 from the program start detection circuit 303. The enabled program circuit 308 analyzes the program signal supplied by the writing device 100 (see FIG. 5) from the output terminal 15, which has become high impedance, and generates a setting signal to be supplied to the microphone amplifier 6 and the transducer bias circuit 8.

In the example shown in FIG. 1, the pull-down switch transistor 11 is an NMOS transistor. The source of the pull-down switch transistor 11 is connected to the ground potential. The gate of the pull-down switch transistor 11 is connected to the control circuit 10 via a pull-down (Pull-DN) control line 20.

One end of the pull-down resistor 12 is connected to the output terminal 15 and the program circuit 308 of the control circuit 10. The other end of the pull-down resistor 12 is connected to the drain of the pull-down switch transistor 11.

Fig. 5 is a diagram showing an example of the configuration of a writing system 1001 that programs the semiconductor integrated circuit 2 provided in the microphone 1 according to the first embodiment. As shown in Fig. 5, the writing system 1001 has a semiconductor integrated circuit 2 provided in the microphone 1 and a writing device 100. The writing system 1001 is a system that programs the semiconductor integrated circuit 2 mounted on the microphone 1 by the writing device 100 from outside the microphone 1.

The writing device 100 is an external device for programming the semiconductor integrated circuit 2 mounted on the microphone 1 from outside the microphone 1. As shown in FIG. 5, the writing device 100 is provided with a current injection control terminal 102, a pull-up control terminal 103, a data (DAT) control terminal 104, and a clock (CLK) control terminal 105. As shown in FIG. 5, the writing device 100 also has a programming power supply 101, inversion circuits 106a, 106b, 106c, and 106d, a data switch transistor 107, a pull-up switch transistor 108, a current injection switch transistor 109, a pull-up resistor 110, a current injection resistor 111, and a clock switch transistor 112.

The input terminals of the inverting circuits 106a, 106b, 106c, and 106d are respectively connected to the current injection control terminal 102, the pull-up control terminal 103, the data control terminal 104, and the clock control terminal 105. The output terminals of the inverting circuits 106a, 106b, 106c, and 106d are respectively connected to the gates of the current injection switch transistor 109, the pull-up switch transistor 108, the data switch transistor 107, and the clock switch transistor 112.

In the example shown in FIG. 5, the data switch transistor 107, the pull-up switch transistor 108, and the current injection switch transistor 109 are each a PMOS transistor. In the example shown in FIG. 5, the clock switch transistor 112 is an NMOS transistor.

The sources of the data switch transistor 107, the pull-up switch transistor 108, and the current injection switch transistor 109 are each connected to the program power supply 101. The drains of the data switch transistor 107, the pull-up switch transistor 108, and the current injection switch transistor 109 are each connected to the drain of the clock switch transistor 112. The source of the clock switch transistor 112 is connected to the ground potential.

The pull-up resistor 110 is connected between the drains of the pull-up switch transistor 108 and the clock switch transistor 112. The current injection resistor 111 is connected between the drains of the current injection switch transistor 109 and the clock switch transistor 112.

When the writing system 1001 programs the semiconductor integrated circuit 2 mounted on the microphone 1, the writing device 100 is connected to the output terminal 18 provided on the housing of the microphone 1. Specifically, as shown in FIG. 5, the drains of the data switch transistor 107, the pull-up switch transistor 108, the current injection switch transistor 109, and the clock switch transistor 112 are connected to the output terminal 18 provided on the housing of the microphone 1.

Here, an example of the operation of the writing system 1001 according to the embodiment will be described with reference to the drawings. FIG. 6 is a diagram showing an example of a signal waveform related to programming of the semiconductor integrated circuit 2 according to the first embodiment.

In the writing system 1001, microphone 1 is a client device that is programmed by a program signal provided by a host device.
In the writing system 1001, the writing device 100 is a host device that externally programs the client device by supplying a program signal to the client device.

The writing device 100 supplies a program signal to the output terminal 18 of the microphone 1, i.e., the output terminal 15 of the semiconductor integrated circuit 2. As shown in FIG. 6, the program signal is composed of a preamble (Preamble), a command (CMD), and data (DAT). In the program signal, an acknowledge (ACK) is provided between each of the preamble, command, and data.

First, the writing device 100 supplies the microphone 1 with a preamble portion for distinguishing the program signal from disturbances other than the program signal. In the example shown in FIG. 6, the writing device 100 executes three current injections by supplying a control signal to the current injection control terminal 102, thereby realizing the preamble of the program signal.

In the semiconductor integrated circuit 2, when a current is applied to the output terminal 15, the microphone amplifier 204 drives the low-side output transistor 205 so as to maintain the voltage of the output terminal 15. As a result, a current equal to the current applied to the output terminal 15 flows through the low-side output transistor 205. At this time, a current of the mirror ratio flows through the current mirror transistor 206 that is mirror-connected to the low-side output transistor 205.

In the semiconductor integrated circuit 2, when the current flowing through the current mirror transistor 206 is greater than the current from the reference current source 207, the input node 208 of the inverting circuit 209 transitions to a low level. Therefore, when the current flowing through the current mirror transistor 206 exceeds the current from the reference current source 207 due to the application of a current to the output terminal 15, the current detection circuit 7 operates to output a high-level current detection signal 13.

The program start detection circuit 303 of the control circuit 10 generates an oscillation enable signal 306 in response to the application of a high-level current detection signal 13, and outputs the oscillation enable signal 306 to the oscillation circuit 307. The oscillation circuit 307 starts oscillating when it receives the oscillation enable signal 306. Specifically, the program start detection circuit 303 transitions the oscillation enable signal 306 output from the output terminal Q of the flip-flop circuit 402 to a high level in response to the high-level current detection signal 13, thereby enabling the oscillation circuit 307.

The program start detection circuit 303 of the control circuit 10 counts the number of pulses in the preamble using a counter composed of flip-flop circuits 401 and 403. When a predetermined number of three pulses are detected by the combination of the flip-flop circuits 401 and 403 and the AND circuit 405, the program start detection circuit 303 transitions the program enable signal 304 to a high level to enable it. When the program enable signal 304 is enabled, the microphone 1 transitions from the normal operation mode to the program mode.

At this time, as shown in FIG. 6, the inversion circuit 302 transitions the signal (EN) supplied to the amplifier operation control terminal 210 to a low level in response to the high-level program enable signal 304 from the program start detection circuit 303. As the signal (EN) supplied to the amplifier operation control terminal 210 transitions to a low level, the output terminal 15 of the microphone amplifier 204, i.e., the output terminal 18 of the microphone 1, becomes high impedance.

The current value of the reference current source 207 is set to output a current with a large current value so that a high-level current detection signal 13 is not generated in the normal operating mode in order to suppress erroneous detection of the program signal. In this situation, the program start detection circuit 303 controls the output terminal 18 to a high impedance in response to the detection of the preamble of the program signal.

This allows the microphone 1 to operate in response to a program signal that includes a predetermined preamble, so as to receive the program signal. Specifically, the program circuit 308 is enabled in response to a program enable signal 304 from the program start detection circuit 303. The program circuit 308 analyzes the program signal from the output terminal 18, which has become high impedance, and generates a setting signal to be supplied to the microphone amplifier 6 and the transducer bias circuit 8.

In addition, when a high-level current detection signal 13 is not applied for a predetermined period of time, the oscillator circuit 307 of the control circuit 10 supplies a timeout signal 305 to the program start detection circuit 303. In response to the timeout signal 305, the program start detection circuit 303 disables the program circuit 308 and stops the high impedance control of the output terminal 18. When the program enable signal 304 is disabled, the microphone 1 transitions from the program mode to the normal operation mode.

If a high-level current detection signal 13 with a predetermined number of pulses (three pulses in FIG. 6) does not appear within a certain period of time, the flip-flop circuits 401, 402, 403, and 404 of the program start detection circuit 303 are reset. In other words, the microphone 1 does not switch to the program mode and maintains the normal operation mode.

In this way, the writing system 1001 according to the embodiment is configured to transition the microphone 1 to the program mode in response to a program signal including a predetermined preamble. This makes it possible to suppress unintended transition to the program mode due to disturbances other than the program signal to the output terminal 15.

In addition, as shown in FIG. 6, the control circuit 10 generates a high-level pull-down signal (Pull-DN) upon detection of the preamble, and supplies the high-level pull-down signal to the gate of the pull-down switch transistor 11 via the pull-down control line 20.

Since the output terminal 18 of the microphone 1 is at high impedance and pulled down, the output terminal 18 is at a low level. In other words, the first half of the acknowledge (ACK0) in FIG. 6 is output from the microphone 1.

Here, in response to the output terminal 18 transitioning to a low level, the writing device 100 supplies a pull-up signal (Pull-UP) to the pull-up control terminal 103, and transitions the output terminal 18 to a midpoint (Mid) potential, which is the divided voltage of the pull-up resistor 110 and the pull-down resistor 12. In response to the voltage of the output terminal 18 reaching the midpoint potential (Mid), the writing device 100 issues an acknowledge (ACK0).

Following the acknowledge (ACK0), the writing device 100 supplies a 1-byte command (in the example of FIG. 6, a 4-bit command (CMD0-3) and address (ADR0-3)) to the output terminal 18 of the microphone 1. The control circuit 10 of the microphone 1 receives the address (ADR0) and transitions the pull-down signal (Pull-DN) to a low level, i.e., releases the pull-down, thereby generating an acknowledge (ACK1).

When the writing device 100 confirms the acknowledgement (ACK1), it supplies one byte of data (DAT0-7) to the output terminal 18 of the microphone 1 by supplying a control signal to the data control terminal 104. As with the command, when the control circuit 10 of the microphone 1 receives the one byte of data, it releases the pull-down to generate an acknowledgement (ACK2).

When the writing device 100 confirms that the output terminal 18 is at a high level in the first half of the acknowledge (ACK2), it transitions the clock signal (CLK) to a low level to generate an acknowledge (ACK2).

In response to the output terminal 18 going high during the first half of ACK2, the program circuit 308 of the control circuit 10 writes the read data (DAT) to ROM or RAM (Random Access Memory). During this write sequence (process), the control circuit 10 generates a high-level pull-down signal (Pull-DN) and releases the pull-down when the write sequence ends.

When the writing device 100 confirms the completion of the writing sequence (process) by the transition of the output terminal 18 to high level, it transitions the clock signal (CLK) to low level and transitions the pull-up signal (Pull-UP) to low level, i.e., releases the pull-up. When it detects the transition of the clock signal (CLK) to low level, the control circuit 10 transitions the signal (EN) supplied to the amplifier operation control terminal 210 to high level, causing the microphone 1 to transition from the program mode to the normal operation mode.

Thus, in the programmable semiconductor integrated circuit 2 according to this embodiment, the control circuit 10 is configured to transition the output terminal 15 to a high impedance state by controlling the microphone amplifier 6 in response to the waveform (current signal) of the current from the output terminal 15. The control circuit 10 is also configured to transition the output terminal 15 to a high impedance state and to start a program operation for setting the transducer bias circuit 8 and the microphone amplifier 6 based on a program signal input from the output terminal 15. With this configuration, the start of programming can be detected based on the currents of the output terminals 15 and 18, making it possible to eliminate the need for a terminal dedicated to programming on the semiconductor integrated circuit 2. Therefore, the technology according to this embodiment can improve the design freedom of the housing of the microphone 1.

In addition, the programmable semiconductor integrated circuit 2 according to this embodiment detects the start of programming based on the current at the output terminals 15 and 18, and is therefore superior to a configuration that detects the start of programming based on the voltage at the output terminals 15 and 18 in the following respects, for example:

For example, in order to improve the accuracy of the program, a so-called trial writing may be performed in which a program value is provisionally written into the semiconductor integrated circuit 2 and then the microphone 1 is actually operated to check whether the desired result is obtained. When performing such trial writing, the program value may be provisionally written and checked several times until the desired result is obtained. Here, the program value is, for example, a set value that specifies the output voltage from the transducer bias circuit 8 that applies a voltage to the microphone transducer 5. In addition, the program value is, for example, a set value that specifies the signal amplification rate of the microphone amplifier 6 that amplifies the signal from the microphone transducer 5 and supplies the amplified signal to the output terminals 15 and 18.

In this situation, in a configuration in which the start of a program is detected based on the state of the output terminals at the time of power-on, such as the voltage of the output terminals 15 and 18, it is necessary to power-on the microphone 1 every time a program operation is started for provisional writing. In addition, when the power is turned on again, the time required to confirm the results of the provisional writing of the program values increases by the time it takes for the microphone 1 to stabilize, which creates the problem that it takes a long time to improve the accuracy of the program. In addition, if the power is turned off, the information from the previous provisional writing is lost, which reduces the efficiency of trial writing.

In contrast, according to the configuration of this embodiment, the start of programming the semiconductor integrated circuit 2, i.e., the transition to the programming mode, can be detected by the current at the output terminals 15 and 18, so programming can be started regardless of the power supply. This makes it possible to use a conventional shipping test system. In addition, it is possible to reduce the total cost related to the semiconductor integrated circuit 2, such as by shortening the development lead time and the programming time.

Second Embodiment
7 is a diagram showing an example of the configuration of a control circuit 10b in a semiconductor integrated circuit 2 according to the second embodiment. The control circuit 10b is an example of the control circuit 10. Here, differences from the first embodiment will be mainly described.

The control circuit 10b in FIG. 7 has a configuration in which, instead of the program start detection circuit 303 and the oscillation circuit 307 in the control circuit 10a in FIG. 3, an oscillation circuit 501 and a counter circuit 503 are included.

The oscillator circuit 501 is connected to the output terminal of the inversion circuit 209 of the current detection circuit 7 and to the counter circuit 503. The oscillator circuit 501 is configured to output a clock signal 502 in response to a high-level current detection signal 13 from the current detection circuit 7.

The counter circuit 503 is connected to the output terminal of the inversion circuit 209 of the current detection circuit 7, the input terminal of the inversion circuit 302, and the program circuit 308. The counter circuit 503 counts the clock signal 502 from the oscillation circuit 501, i.e., the current injection time. When the count reaches an arbitrary count, the counter circuit 503 generates a program enable signal 304 and simultaneously transitions the amplifier operation control terminal 210 to a low level, controlling the output terminal 15 (output terminal 18) to a high impedance.

Figure 8 is a diagram showing an example of the configuration of the counter circuit 503 in the control circuit 10b of Figure 7. As shown in Figure 8, the counter circuit 503 has flip-flop circuits 601, 602, and 603, a logical product circuit 604, and inversion circuits 605, 606, and 607.

Flip-flop circuits 601 and 602 form a counter similar to flip-flop circuits 401 and 403 in FIG. 4. For example, inversion circuits 605 and 606 are similar to inversion circuits 406 and 407 in FIG. 4, respectively. Flip-flop circuits 601 and 602 are generally similar to flip-flop circuits 401 and 403 in FIG. 4, respectively.

However, the reset terminals RST of the flip-flop circuits 601 and 602 are connected to the output terminals of the inversion circuit 607 instead of the oscillation circuit 307, and the current detection signal 13 from the current detection circuit 7 inverted by the inversion circuit 607 is input. Also, the clock input terminal CK of the flip-flop circuit 601 is connected to the oscillation circuit 501 instead of the current detection circuit 7, and the clock signal 502 is input.

It is also possible to set any number of count digits by connecting similar flip-flop circuits in multiple stages between flip-flop circuits 601 and 602. In this case, an inversion circuit similar to inversion circuits 605 and 606 is provided for each flip-flop circuit.

The input side of the logical product circuit 604 is connected to the output terminal Q of each of at least two flip-flop circuits including the flip-flop circuits 601 and 602, in the same manner as the logical product circuit 405 in FIG. 4.

Figure 9 shows an example of a signal waveform related to programming of the semiconductor integrated circuit 2 according to the second embodiment.

The program signal according to this embodiment differs from the program signal according to the first embodiment in terms of the preamble.

The counter circuit 503 is in a reset state when the current detection signal 13 is at a low level, and starts counting in response to a high-level current detection signal 13. Specifically, the oscillation circuit 501 outputs a clock signal 502 in response to a high-level current detection signal 13 from the current detection circuit 7. The counter circuit 503 also counts the clock signal 502 from the oscillation circuit 501.

When the counter circuit 503 reaches a desired count, it generates a high-level program enable signal 304 and enables the program circuit 308. At the same time as enabling the program circuit 308, the counter circuit 503 transitions the amplifier operation control terminal 210 to a low level and controls the output terminal 15 to a high impedance. In the configuration of FIG. 8, when the counter value reaches all 1s, the AND circuit 604 updates the data in the flip-flop circuit 603 and transitions the program enable signal 304 to a high level. The time for detecting the current detection signal 13 can be arbitrarily controlled by setting the number of digits of the count value.

In the example shown in FIG. 9, when the counter circuit 503 counts to "5", at the next timing "6", the control circuit 10 of the microphone 1 transitions the pull-down signal (Pull-DN) to a high level and transitions the signal (EN) supplied to the amplifier operation control terminal 210 to a low level, putting the output terminal 15 of the microphone amplifier 204, i.e., the output terminal 18 of the microphone 1, into a high impedance state.

In this way, the control circuit 10b according to this embodiment is configured to detect a preamble based on the time (current injection time) during which a high-level current detection signal 13 is detected. Even with this configuration, it is possible to suppress unintended transition to the program mode due to disturbances other than the program signal at the output terminal 15, just like the control circuit 10a according to the first embodiment, which detects a preamble based on the number of pulses (current signal) of a high-level current detection signal 13.

The control circuit 10a according to the first embodiment and the control circuit 10b according to the second embodiment can be combined as appropriate. For example, the program enable signal 304 may be generated based on at least one of the number of pulses in the preamble portion of the program signal input to the output terminal 15 and the current injection time.

As described above, the semiconductor integrated circuit 2, microphone 1, and writing system 1001 according to the embodiment allow the semiconductor integrated circuit 2 to be programmed without providing a dedicated terminal.

Although the embodiments of the present invention have been described above, the above embodiments are presented as examples and are not intended to limit the scope of the invention. The above novel embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the gist of the invention. These embodiments are included in the scope and gist of the invention, and are included in the scope of the invention and its equivalents described in the claims.

LIST OF SYMBOLS 1 Microphone 2 Semiconductor integrated circuit 3 Microphone signal input terminal 4 Microphone bias terminal 5 Microphone transducer 6 Microphone amplifier 7 Current detection circuit 8 Transducer bias circuit 9 Set value signal node 10 Control circuit 11 Pull-down switch transistor 12 Pull-down resistor 13 Current detection signal 14, 17 Power supply terminal 15, 18 Output terminal 16, 19 Ground terminal 20 Pull-down (Pull-DN) control line 100 Writing device 101 Program power supply 102 Current injection control terminal 103 Pull-up (Pull-UP) control terminal 104 Data (DAT) control terminal 105 Clock (CLK) control terminal 106a, 106b, 106c, 106d, 209, 302, 406, 407 Inverting circuit 107 Data switch transistor 108 Pull-up switch transistor 109 Current injection switch transistor 110 Pull-up resistor 111 Current injection resistor 112 Clock switch transistor 201 High-side output transistor 202 Feedback circuit 203 Microphone signal input terminal 204 Microphone amplifier 205 Low-side output transistor 206 Current mirror transistor 207 Reference current source 208 Input node 210 Amplifier operation control terminal 303 Program start detection circuit 304 Program enable signal 305 Time-out signal 306 Oscillation enable signal 307, 501 Oscillation circuit 308 Program circuit 401, 402, 403, 404, 601, 602, 603 Flip-flop circuit 405, 604 Logical AND circuit 502 Clock signal 503 Counter circuit 1001 Write system

Claims (5)

a transducer bias circuit for applying a voltage to the microphone transducer;
a microphone amplifier that amplifies a signal from the microphone transducer and supplies the amplified signal to an output terminal;
a current detection circuit connected between the microphone amplifier and the output terminal, the current detection circuit detecting a current from the output terminal;
a control circuit that transitions the output terminal to a high impedance state by controlling the microphone amplifier in response to a current signal from the output terminal, and that starts a program operation for setting the transducer bias circuit and the microphone amplifier based on a program signal input from the output terminal. The semiconductor integrated circuit according to claim 1, wherein the control circuit has a program start detection circuit that counts the number of pulses contained in the current signal from the output terminal and generates a program enable signal that starts the program operation when the number of pulses reaches a predetermined number. The semiconductor integrated circuit according to claim 1 or 2, wherein the control circuit has a counter circuit that counts the injection time of the current from the output terminal based on the current signal from the output terminal, and generates a program enable signal that starts the program operation when the injection time reaches a predetermined time. A semiconductor integrated circuit according to any one of claims 1 to 3;
a microphone transducer connected between the microphone amplifier and the transducer bias circuit. A semiconductor integrated circuit according to any one of claims 1 to 3;
a writing device connected to the output terminal of the semiconductor integrated circuit and supplying the program signal to the output terminal.

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