JPH061888B2 - Schmitt circuit - Google Patents

Description

The present invention relates to a Schmitt circuit using a MOS transistor.

[Prior Art] A conventional Schmitt circuit is shown in FIG. A conventional Schmitt circuit with a high threshold voltage accuracy is shaped by using two comparator circuits 11 and 12 to which reference voltages V _H and _VL obtained by resistance division are given together with an input signal and the outputs of these comparator circuits as inputs. It is composed of an RS flip-flop circuit 13 that outputs a different waveform.

[Problems to be Solved by the Invention] The Schmitt circuit shown in FIG. 9 consumes a large amount of power as well as a large chip area because it uses two analog comparison circuits.

Considering the above drawbacks, a Schmitt circuit as shown in FIG. 10 in which one comparator circuit is provided is conceivable. In this circuit, the reference voltages V _H and V are provided between the reference voltage generation circuit 16 and the comparison circuit 14.
_A switch circuit 15 for switching _L is provided. Comparison circuit 14
Receives an input signal and one reference voltage connected by the switch circuit 15, and outputs an output signal of the Schmitt circuit and a control signal of the switch circuit.

The Schmitt circuit of FIG. 10 solves the problems of increased power consumption and chip area. However, since the switch circuit 15 is directly connected to the reference voltage generation circuit 16, parasitic capacitance and The mirror capacitance of the switch transistor causes charging and discharging during switching, which causes noise. When a large number of Schmitt circuits are shared, this noise may affect the threshold voltage of other Schmitt circuits and cause malfunction.

[Means for Solving the Problems] In order to achieve the above object, in the present invention, a constant current source circuit connected to a first power supply and a reference voltage generating circuit for generating a first reference voltage and a second reference voltage. Connected to the circuit and the second power supply,
A first input terminal, a second input terminal and one output terminal,
Between a comparison circuit that differentially outputs an input signal to the first input terminal and an input signal to the second input terminal from the output terminal, and between the constant current source circuit and the first input terminal of the comparison circuit. First MOS provided and having an input signal applied to its gate
A transistor, a second MOS transistor provided between the constant current source circuit and a second input terminal of the comparison circuit and having the gate to which the first reference voltage is applied; a second of the constant current source circuit and the comparison circuit; The second MOS is provided between the input terminals.
A third MOS transistor provided in parallel with the transistor and having a gate to which the second reference voltage is applied;
One of a signal passing through the second MOS transistor and a signal passing through the third MOS transistor is provided between the OS transistor and the second input terminal of the comparison circuit, and depending on the output signal supplied from the output terminal of the comparison circuit. Is provided to the second input terminal of the comparison circuit, and a switch circuit for controlling the input to be input to the second input terminal of the comparison circuit.

[Operation] In the Schmitt circuit configured as described above, the MOS transistor to which the input signal is applied to the gate and the MOS transistor connected to the comparison circuit by the switch circuit and having one reference voltage applied to the gate are differential. Works as a circuit. The currents from both transistors are compared in a comparison circuit,
The comparison circuit outputs an output signal and a control signal for the switch circuit. When the input signal changes and the output of the comparison circuit is inverted, the switch is switched, and this time the input signal is applied to the MOS.
The transistor and the MOS transistor to which the other reference voltage is applied form a differential circuit. Similarly, the current is input to the comparison circuit, and the output signal of the Schmitt circuit and the control signal of the switch circuit are obtained.

In this way, the signal is inverted with the voltage V _H or V _L that serves as the threshold value of the Schmitt circuit, and the waveform-shaped signal is output.

[Embodiment] This embodiment will be described below with reference to the drawings.

FIG. 1 is a diagram showing the operating principle of an embodiment of the present invention. In the figure, Tr1, Tr2 and Tr3 are all MOS transistors of the same channel type, and an input signal is applied to the gate of Tr1. The constant current circuit 1 is connected to the power source V _B1 and Tr
A constant current is supplied to the common source of 1, Tr2 and Tr3.
The reference voltage generation circuit 2 outputs the reference voltages V _H and V _L to T
It is applied to the gates of r2 and Tr3. (However, V _H > V _L
And The switch circuit 3 connects Tr3 to the comparison circuit 4 when the control signal from the comparison circuit is at "H" level, and connects Tr2 to the comparison circuit 4 when the control signal is at "L" level.
The comparison circuit 4 inputs the current input from Tr1 to the “−” terminal, and
The current input from r2 or Tr3 is received by the "+" terminal, and both are compared, and the "H" level is output when the "+" terminal is large, and the "L" level is output when the "-" terminal is large. To the switch circuit 3.

FIG. 2 shows a concrete circuit diagram of the embodiment shown in FIG. The T
r1, Tr2, Tr3 are composed of P-channel MOS transistors. The constant current circuit 1 includes a P-channel MOS transistor Tr4 having a gate to which a voltage source V _B1 is applied.
Composed of. The reference voltage generating circuit includes power supplies V _DD and V
It is composed of a resistor provided between _SS , and this resistor is divided to obtain reference voltages V _H and V _L. The switch circuit 3 is connected to the terminal 6 and is connected in parallel to the P channel M.
An OS transistor Tr5, a channel MOS transistor Tr6, and a transfer gate composed of an inverter provided between the gate of Tr5 and the gate of Tr6. Connected to. The comparison circuit 4 is connected to the terminal 8 and serves as a "+" terminal. The P-channel MOS transistor Tr is connected to the drain and the gate.
8 and a P-channel MOS transistor Tr9 having a gate connected to the drain of Tr8, and a P-channel MOS transistor T having a drain and a gate connected to the terminal 7 and serving as a "-" input terminal.
A current mirror circuit composed of r7 and a P-channel MOS transistor Tr10 having a gate connected to the drain of Tr7, and a N-channel MOS transistor having a drain connected to the drain of Tr9, a gate connected to the drain, and a source connected to a power supply. Tr11 and drain are T
N-channel MOS whose drain is connected to r10, whose gate is connected to the drain of Tr11, and whose source is connected to the power supply
And a current mirror circuit including a transistor Tr12. The comparison circuit 4 draws a current flowing through the Tr12 as compared with the "+" terminal input current and a current flowing through the Tr10 in proportion to the "-" terminal input current when they flow into the output terminal, and the "+" terminal When the input current is larger than the "-" terminal input current, "H" level is output, and when the "-" terminal input current is larger, "L" level is output.

Next, the operation will be described. Here, a case where the difference between the reference voltages V _H and V _L is large will be described.

When the input signal changes from V _DD to V _SS (however, V
_DD > V _SS ) When V _DD is applied to the input terminal IN in the initial state, Tr1 is off and no current flows through the “−” terminal of the comparison circuit. On the other hand, the "+" terminal of the comparison circuit has T
A current flows through r2 or Tr3, and the comparison circuit 4 outputs the “H” level to the output terminal OUT and the switch circuit 3. When the switch circuit 3 enters the “H” level, Tr5,
Tr6 is turned on and Tr3 is connected to the "+" terminal. In this embodiment, the difference between the reference voltages V _H and V _L is set to be large. This is because Tr2 and Tr3 have a common source and drain, and when V _L is significantly smaller than V _H, Tr3 is sufficiently ON. On the contrary, Tr2 is turned off, and it works as if only Tr3 is connected. Therefore, Tr1 and Tr3 work as a differential circuit. When the input signal decreases and becomes _VL or less, the "-" terminal input current of the comparison circuit increases due to the "+" terminal input current, the comparison circuit is inverted, and the output terminal OUT becomes "L" level Tr5 of the switch circuit. And Tr6 turn off and Tr
Connect the 2 side to the comparison circuit. Therefore, Tr1 and Tr2 work as a differential circuit. Even if the input signal further decreases to _VSS , this state is maintained because the "-" terminal input current is larger than the "+" terminal input current.

Next, a case where the input signal changes from V _SS to V _DD will be described. When V _SSH is applied to the input terminal IN, “L” level is applied to the output terminal OUT, Tr1 is connected to the “−” terminal of the comparison circuit, and Tr2 is connected to the “+” terminal. When the input signal increases and becomes V _H or more, the input current of the “+” terminal of the comparison circuit becomes larger than the input current of the “−” terminal. Then, the output of the comparison circuit changes from the “L” level to the “H” level, the “H” level is added to the output terminal OUT, the Tr5 and Tr6 of the switch circuit are turned on, and Tr3 becomes the “+” terminal of the comparison circuit. Connected. Therefore T
The differential circuit of r1 and Tr3 works, and this state is maintained even if the input signal further increases to V _DD .

As described above, the high-precision Schmitt circuit in which the high level input threshold is V _H and the low level input threshold is V _L can be configured. The conventional comparison circuit in the circuit shown in FIG. 10 is configured by including a constant current source and a differential circuit including two transistors in the comparison circuit of the above embodiment. Therefore, the present invention can provide a Schmitt circuit that is not easily affected by noise generated when one reference voltage generating circuit is shared with the same number of elements as the circuit of FIG.

Another embodiment will be described below.

An embodiment of the switch circuit is shown in FIG. 3, FIG. 4 and FIG. FIG. 3 shows two sets of P-channel and N-channel MOS transistors Tr13 and Tr14, Tr1 connected in parallel.
5 and Tr16, the common gate of Tr13Tr16 and Tr
An inverter provided between the common gates of 14Tr15, the source of Tr13 and the drain of Tr14 are commonly connected to the terminal 5, and the source of Tr15 and the drain of Tr16 are commonly connected to the terminal 6. On the other hand, the drain of Tr13, the source of Tr14, the drain of Tr15, and the source of Tr16 are commonly connected to the terminal 8. The operation is Tr13 and T when the control signal is at "H" level.
r14 turns off, Tr15 and Tr16 turn on and Tr
When the 3 side is connected and the control signal is at "L" level, Tr13
Since Tr14 is turned on and Tr14 and Tr15 are turned off, the Tr2 side is connected. The switch circuits shown in FIGS. 4 and 5 each have a configuration in which the P-channel MOS transistor is removed. When operating the source voltage of the N-channel MOS transistor in the range close to V _SS , sufficient switching operation can be obtained without connecting the P-channel MOS transistor.

Another embodiment of the comparison circuit is shown in FIGS. 6, 7 and 8. FIG. 6 shows an inverter added to the output of the comparison circuit described in the embodiment of FIG. Output terminal OUT
When a large load is applied, for example, when the wiring connected to is long or when the gate capacitance is large, a delay occurs in the comparison circuit of FIG. 2 and the current driving force decreases. Therefore, in the comparison circuit of FIG. 6, an inverter having a small input capacitance can be added to the output section to increase the current driving force when the load applied to the output of the Schmitt circuit is large. The comparison circuit shown in FIG. 7 includes a current mirror circuit and an amplifier circuit. The N-channel MOS transistor Tr17 whose drain is connected to the terminal 7 and the N-channel MOS transistor Tr18 whose drain is connected to the terminal 8 and the gate are An N-channel MOS transistor T whose gates are commonly connected to form a current mirror circuit and whose gate is connected to the terminal 7.
r19 and a P channel M to which the power source V _B2 is applied to the gate
The OS transistor Tr20 is connected in series and constitutes a grounded-source amplifier circuit. "+" Terminal 8 input power is T
Tr19 is set by the current mirror circuit of r17 and Tr18.
Pull the gate to _{V SS} side. On the other hand, the input current of the “−” terminal 7 pulls the gate of the Tr 19 toward the V _DD side. When the input current of the “−” terminal 7 is larger than that of the “+” terminal 8, the gate voltage of the Tr 19 becomes high and the Tr 19 is turned on and outputs the “L” level. Conversely, the input current of the "+" terminal 8 is "-".
When it is larger than the input current of the terminal 7, the gate voltage of the Tr 19 becomes low and turned off to output the “H” level. 8th
As in the case of FIG. 6, the output of the comparison circuit of FIG. 7 can be loaded with an inverter and the connection of the current input can be reversed to increase the current driving force. The current comparison circuit as shown in FIGS. 7 and 8 is inferior in speed to the comparison circuit used in FIG. 2, but can be simply constructed.

Next, as another embodiment of the Schmitt circuit, a case where the connection between the MOS transistor and the comparison circuit in FIG. 1 is reversed will be described. That is, Tr1 is connected to the "+" terminal 8 of the comparison circuit, a signal for switching Tr2 or Tr3 is electrically connected to the "-" terminal 7 of the comparison circuit, and the control signal of the switch circuit is inverted and input by an inverter or the like. Do or T
The connection between the drains of r2 and Tr3 and the input of the switch circuit is reversed. The circuit as described above obtains an output having a phase opposite to that of the output of the circuit of FIG. 1 by the same operation as the circuit of FIG.

The present invention can be configured by combining the switch circuit and the current comparison circuit of the above embodiments. Further, the present invention is not limited to the above embodiment, and
Channel (or N-channel) MOS transistor N
The same effect can be obtained by using a channel (or P-channel) MOS transistor.

[Effects of the Invention] As described above, according to the present invention, a large number of Schmitt circuits can be commonly used in one reference voltage generation circuit to obtain accurate operation, and a small chip area and high power consumption with high accuracy can be obtained. A Schmitt circuit can be provided.

[Brief description of drawings]

FIG. 1 is a diagram showing the principle of operation of the present invention, FIG. 2 is a block diagram of an embodiment of the present invention, and FIGS. 3, 4 and 5 are other embodiments of the switch circuit portion of the present invention, and FIG. FIG. 7, FIG. 7 and FIG. 8 are other embodiments of the comparison circuit unit of the present invention, and FIG. 9 and FIG. 1 ... Constant current source circuit 2 ... Reference voltage generation circuit 3 ... Switch circuit, 4 ... Comparison circuit 5-10 ... Terminals Tr1 to Tr20 ... MOS transistor.

Claims (2)

[Claims] 1. A constant current source circuit connected to a first power supply, a reference voltage generation circuit for generating a first reference voltage and a second reference voltage, a second power supply, a first input terminal and a second input terminal. An input terminal and one output terminal are provided, and an input signal to the first input terminal and an input signal to the second input terminal are compared by a current,
A comparator circuit for differentially outputting from the output terminal; a first MOS transistor having a gate to which an input signal is applied provided between the constant current source circuit and a first input terminal of the comparator circuit; and the constant current source circuit And a second M connected to the second input terminal of the comparison circuit and having the gate to which the first reference voltage is applied.
An OS transistor, a third MOS transistor connected to the constant current source circuit and having a gate to which the second reference voltage is applied, a second input terminal, an output terminal of the comparison circuit, and the third transistor
An output signal that is connected to a MOS transistor, forms a current path of a current flowing from the constant current source circuit through the third MOS transistor to the second input terminal of the comparison circuit, and is supplied from the output terminal of the comparison circuit. And a switch circuit that opens and closes the current path in response to the above. 2. A constant current source circuit connected to a first power supply, a reference voltage generation circuit for generating a first reference voltage and a second reference voltage, a second power supply, a first input terminal and a second input terminal. An input terminal and one output terminal are provided, and an input signal to the first input terminal and an input signal to the second input terminal are compared by a current,
A comparator circuit for differentially outputting from the output terminal; a first MOS transistor provided between the constant current source circuit and a first input terminal of the comparator circuit to which an input signal is applied to a gate; and the constant current source circuit. A second M provided between the second input terminals of the comparison circuit and having the gate to which the first reference voltage is applied.
An OS transistor is provided in parallel with the second MOS transistor between the constant current source circuit and the second input terminal of the comparison circuit, and the second MOS transistor is provided in parallel with the second MOS transistor.
A third MOS transistor having a gate to which a reference voltage is applied, the second and third MOS transistors and a second input terminal of the comparison circuit, and the second MOS according to an output signal supplied from an output terminal of the comparison circuit. A Schmitt circuit, comprising: a switch circuit for controlling one of a signal passing through a transistor and a signal passing through the third MOS transistor to be input to the second input terminal of the comparison circuit.