JPS6147017B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an output section of an integrated circuit, and more particularly to a demodulation output section of an FM demodulation circuit.

A signal input to the integrated circuit is processed by an internal signal processing circuit, and a desired output signal appears at the load resistor, but an undesired output may appear due to current changes within the integrated circuit. This becomes noticeable when an electronic switching circuit that switches part of the operation of the signal processing circuit is included. Integrated circuit devices including switching circuits are often used as FM demodulation circuits, squelch circuits, various automatic switching circuits, and their display circuits.

When the internal current is changed due to the operation of the switching circuit and noise is generated, the quality of the analog signal deteriorates. Specifically, in the case of a circuit that handles audio signals, this noise is output as a harsh shock sound from a speaker, etc., which is not only unpleasant, but may even damage the speaker. In the case of television, the screen becomes blurred.

When we investigated the cause of this, we found that when the switching circuit directly intermittents the analog signal, the superimposed DC component also intermittents, resulting in a change in the DC component, which is differentiated by the coupling capacitor and amplified in the subsequent stage. For example, a change in the current flowing through the common wiring of a circuit may cause a voltage change in the wiring resistance or the internal resistance of the power supply, which may affect the circuit that handles analog signals. I found out. The present invention relates to the latter solution.

FIG. 1 is a block diagram of a conventional FM stereo broadcast multiplex demodulator. 1 is the power supply, its internal resistance and the resistance associated with wiring (equivalently 2
) is applied to the power supply terminal 5 on the external shape (on the lead frame) of the integrated circuit device 4 . Also, power supply 1 has capacitor 3 for AC component.
is bypassed. The voltage applied to the terminal 5 is applied to the lead-out terminal (bonding wire) on the integrated circuit board via a minute resistance (equivalently indicated by 6) present in the lead-out wire (bonding wire), etc.
7 and is supplied as a power source to each block in the integrated circuit. Similarly, the ground terminal is grounded from the lead-out terminal 8 on the integrated circuit board through a resistance associated with wiring (equivalently indicated by 9) and a terminal 10 on the outside. On the other hand, the FM detected signal 11 is passed through a coupling capacitor 12 to an input terminal 13 (correctly, this part can be divided into a terminal on the outside and a terminal on the board, but the latter is omitted because it is not directly related to the present invention. ) to the emitter follower circuit 15 in the integrated circuit device,
Its output is transmitted to the demodulation circuit 16 and the subcarrier regeneration circuit 23.
and are added to each. The demodulation circuit 16 multiplies the reproduced subcarrier and the output signal of the emitter follower circuit 15, and outputs terminals 17 and 18 on the outer shape.
A demodulated output is obtained at both ends of load resistors 19 and 21. Note that the capacitors 20 and 22 are for de-emphasis. Here, the carrier wave regeneration circuit 23 doubles the pilot signal, but at this time there are components 25, 27 and 28 that cannot be built into the integrated circuit, and these components are connected to the power supply 1 without going through the power supply and ground terminals 5 and 10. It has a path that is connected to or grounded. 29 indicates whether there is a pilot signal or manually switches between stereo and monaural, and an indicator lamp 31
This is an electronic switching circuit that drives the 33 and 34 are signal output terminals to the next stage. Further, 14 is a voltage stabilizing circuit.

In such a circuit configuration, noise is generated every time the switching circuit 29 switches, and the noise is amplified in a subsequent stage (not shown), producing unpleasant sound from the speaker. One of the reasons for this is that, due to the structure of the integrated circuit device, it is necessary to lead out the lead-out terminals 7 and 8 on the board to the terminals 5 and 10 on the outside using thin wires.
There are minute resistances 6 and 9, and there is a difference in the DC component of the current supplied from the power supply to the subcarrier regeneration circuit 23, switching circuit 29, etc. before and after switching, and the terminals 24 and 2
There is also a difference in the DC component of the current flowing through the power supply terminal 5 and the ground terminal 10, which causes a difference in the DC component of the current flowing through the power terminal 5 and the ground terminal 10, and the voltage generated across the microresistors 2, 6, 9, etc. fluctuates. be. Now, the resistance value
If there is a current change of 10 to 100 mA before and after switching at 0.5Ω, a voltage change of several tens of mVpp will occur.

Considering the influence of the minute resistance on the power supply side, the voltage drop at terminal 33 due to fluctuations in voltage drop due to internal resistance 2 of the power supply
And the DC voltage between 34 and ground continues to fluctuate. This is because even if the voltage at the lead-out terminal 7 on the board fluctuates somewhat, the current flowing through the terminals 17 and 18 is kept almost constant due to the voltage stabilizing circuit 14, so that the resistances 19 and 21 due to these currents are This is because the voltage at both ends is approximately constant. In other words, the voltage change occurring in the internal resistance 2 of the power supply appears directly between the output terminals 33, 34 and the ground. The sum of these voltage changes is differentiated by a coupling capacitor, etc., and the 40 dB is added after terminals 33 and 34.
Since the signal is amplified by an amplifier circuit with a gain higher than that, a voltage sufficient to produce an unpleasant sound is applied to the speaker.

SUMMARY OF THE INVENTION An object of the present invention is to provide an integrated circuit that prevents voltage fluctuations caused by power source impedance from appearing in output signals due to changes in the current flowing through the integrated circuit.

According to the present invention, the output signal of the signal processing circuit is changed in current by a current mirror circuit, the current is supplied to a load resistor whose one end is connected to a reference potential (ground potential), and the signal obtained at this load resistor is Obtain an integrated circuit that outputs as an output signal.

In the present invention, the signal is once supplied to the current mirror circuit, and the current amplification factor is determined by the shape of the element and is not affected by fluctuations in the power supply.Moreover, one end of the current passing through the current mirror circuit is connected to a reference potential point. It is supplied to a load resistor and taken out as an output. Therefore, fluctuations in power supply voltage due to power supply impedance are not easily affected, and noise generation can be suppressed.

The present invention will be described in detail below with reference to the drawings.

FIG. 2 is a block diagram of an FM stereo broadcast multiplex demodulator to which the present invention is applied.
FIG. 3 is a detailed circuit diagram thereof. The same symbols indicate the same thing. 401~
Reference numeral 409 denotes an element constituting the voltage stabilizing circuit 14, which keeps the emitter voltages of the transistors 402 and 404 at a constant value. 410 to 415 constitute an emitter follower circuit 15, which converts the input signal from the terminal 13 into impedance and converts it into the demodulation circuit 1.
6 and the subcarrier regeneration circuit 23. 46
7 is a terminal to which an external capacitor 468 is connected. 416 to 426 are elements constituting a switching type demodulation circuit 16 widely used in integrated circuits. 431 to 444 are subcarrier regeneration circuits 2
The transistor 439 amplifies the input signal, the external tuning circuit 25 selects the pilot signal, the transistors 434 and 436 perform class C amplification, the diodes 443 to 444 shape the signal, and the transistor 441 amplifies the input signal. It is multiplied and a reproduced subcarrier wave is obtained by an external 38KHZ tuning circuit 464. A portion of the pilot signal is rectified by transistor 438 and applied to switching circuit 29. It is smoothed by a capacitor 466 connected to a terminal 465 (this is also a connection terminal for a manual stereo monaural changeover switch 467), and 449 to 453.
In addition to the Schmitt trigger circuit consisting of
The output drives the lamp drivers 454 to 456 to blink the lamp 31, and is applied to the transistor 446 to switch the subcarrier regeneration circuit 23 into operation or non-operation.

The major difference from FIG. 1 is the output extraction configuration of the demodulation circuit 16. That is, one output (left channel output) of the demodulation circuit 16 is connected to the diode 35.
1. Transistor 352 and resistors 427, 42
It is converted into a current by a current mirror circuit consisting of 8,
The current is supplied to a load resistor 319 connected at one end to ground terminal 308. The other end of resistor 319 is connected to output terminal 317. Similarly, the other output (right channel output) of the demodulation circuit 16 is connected to the diode 353, the transistor 354, and the resistor 42.
The current is supplied to a current mirror circuit consisting of 9,430 and converted into a current, and the current is supplied to a load resistor 321 whose one end is connected to the ground terminal 308 and the other end is connected to the output terminal 318.

In this configuration, the bias of the output current of the demodulator 16 is stabilized by the voltage stabilization circuit 14 as in the conventional case, so even if the power supply voltage fluctuates, the output current remains almost constant in both DC and AC. It is. In addition, a diode 351 made on the same substrate,
Since the transistors 353 and the transistors 352 and 354 have a constant current amplification factor determined by the emitter area ratio, a voltage proportional to the output current of the demodulator 16 is generated in the loads 319 and 321. This is insensitive to fluctuations in power supply voltage. Therefore, when switching, power supply 1
Even if the potentials of the terminal 5 and the lead-out terminal 7 change due to the internal resistance 2 and microresistance 6, the DC component of the voltage of the output terminals 33 and 34 does not change as in the conventional case. Output terminals 320 and 322 on the outside are de-emphasis capacitors 317 and 318, respectively. In this way, it was possible to reduce the noise generated during switching.

Note that the DC component of the output voltage has some dependence on the power supply voltage due to the dynamic resistance of the constant voltage element, etc.
In reality, the fluctuation is about 1/30 of the power supply voltage fluctuation, so 1/30 of the voltage fluctuation occurring in the internal resistance 2 of the power supply 1 occurs in the output at the time of switching, but it is sufficiently small and can be ignored.

Further, as shown in FIGS. 2 and 3, two ground terminals 308 and 355 are provided. This prevents the potential of the ground line from fluctuating due to the operation of the switching circuit 29. That is, the signal input is a signal source 11, a capacitor 12, a terminal 13, an emitter follower circuit 15, and a grounding terminal 30.
8 (its resistance is equivalently designated 309), terminal 3
The current flowing through the microresistance 309 does not change before and after switching between stereo and monaural, so the voltage across the resistor is constant, and the input The switching circuit has no influence through the switching circuit. Specifically, such a resistor includes a voltage stabilizing circuit 14, an emitter follower 15, a demodulating circuit 16, and loads 319 and 32.
1 and the emitter current of the first-stage transistor 439 of the subcarrier regeneration circuit 23 are flowing, and neither of them changes due to the switching operation.
The remaining part is the second ground lead-out terminal 355
(equivalent resistance 356) and the external terminal 357, the potential of the grounding terminal 356 changes every time the subcarrier regeneration circuit 23 and the switching circuit 29 are connected on the board. Since a closed circuit is formed, the operation of such a circuit does not depend on slight fluctuations in potential.

As described above, according to the present invention, it is possible to provide a circuit that is not affected by voltage fluctuations due to power source impedance. Changes in the DC component during switching are a problem, but changes in the AC component are not a problem because they are usually absorbed by the bypass capacitor (3 in FIGS. 1 and 3) of the power supply. However, if excessive current flows during switching, for example when a capacitor is charged or discharged, a DC component will be generated transiently, so these currents should be passed through the ground lead wire of the analog signal system mentioned above. must not.

[Brief explanation of the drawing]

Fig. 1 is an example of a block diagram of a conventional FM stereo broadcast multiplex demodulator, Fig. 2 is an example of a block diagram of an FM stereo broadcast demodulator to which the present invention is applied, and Fig. 3 is a detail of Fig. 2. This is a circuit diagram. 1 is a power supply, 2 is an equivalent representation of its internal resistance, 4 is an integrated circuit device, 6 and 9 are equivalent representations of the resistance of the power supply and ground lead wires, and 7 and 8 are equivalent representations of the resistance. Extraction terminals (bonding pads) on the board, 5 and 10
14 is a voltage stabilizing circuit, 15 is an emitter follower circuit, 16 is a terminal on the outer shape (on a lead frame), and 15 is an emitter follower circuit.
23 is a demodulation circuit, 23 is a subcarrier regeneration circuit, 29 is a switching circuit, 20 and 22 are load resistors, 31 is a lamp, and 33 and 34 are signal output terminals to the next stage.

Claims (1)

[Claims] 1. An integrated circuit device comprising a signal processing circuit and a switching circuit connected between a power supply terminal and a reference potential supply terminal and switching the operation of the signal processing circuit in response to a control signal, the integrated circuit device comprising: a current mirror circuit coupled between an output terminal and the power supply terminal and receiving an output signal current from the signal processing circuit and generating a corresponding signal current; an output terminal of the current mirror circuit and the reference potential; An integrated circuit device further comprising: a load resistor connected between the load resistor and the supply terminal; a signal output terminal; and means for supplying a signal obtained at the load resistor to the signal output terminal.