JPH0488708A - Switching circuit - Google Patents

Abstract

PURPOSE:To reduce the distortion factor by inputting an input signal to a noninverting input terminal of an operational amplifier circuit via a 1st switch circuit section and feeding back an output signal to an inverting input terminal via a 2nd switch circuit section. CONSTITUTION:An input signal S1(S2) is inputted to a noninverting input terminal of an operational amplifier 22 via a 1st switch circuit section 4(6) and an output signal S0 of the operational amplifier circuit 22 is fed back to an inverting input terminal via a 2nd switch circuit section 24. Thus, a resistance of a feedback resistor is varied in response to a change in an on-resistance of the switch circuit section 4(6) and the switch circuit is applied to a general analog circuit to reduce the distortion factor.

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to a switch circuit, and can be applied to, for example, switching an electronic volume or switching the gain of a variable gain amplifier circuit.

B. Summary of the Invention The present invention provides a switch circuit in which an input signal is output through a buffer circuit made of an operational amplifier circuit, and is input to a non-inverting input terminal of the operational amplifier circuit through a first switch circuit section. At the same time as inputting the signal, the second
By feeding back the output signal through the switch circuit section, the distortion factor can be reduced compared to the conventional method.

BACKGROUND ART Conventionally, for example, when incorporating a switch circuit into an integrated circuit that processes an analog signal, a P-channel MOS (metal oxide semiconductor) as shown in FIG.
(onductor) transistor and an N-channel MOS transistor are combined to form a switch circuit.

That is, in the P-channel MO3) transistor 1 and the N-channel MO3) transistor 2, the sources and drains are commonly connected and assigned to analog signal input/output terminals, respectively.

In this state, control signals Q and IQ having different polarities are applied to the gates of P-channel MOS transistor 1 and N-channel MOS transistor 2.

This allows the polarities of the control signals Q and IQ to be switched simultaneously to switch the on/off state.

D Problems to be Solved by the Invention However, in this type of switch circuit, as shown in FIG. 5, the on-resistance inevitably changes depending on the signal level of the input signal.

Therefore, when the load resistance connected to the switch circuit is small, there is a problem in that nonlinear distortion occurs.

That is, as shown in FIG.
and 6 to selectively input two input signals S1 and S2, and output them to the amplifier circuit via a load resistor 8.

At this time, the amplitude level of input signal S1 or S2 is ±2 [■
], the on-resistance of about 2 (kΩ) at 0 (■) becomes -2 (
■] changes to approximately ICkΩ].

Therefore, if a load resistor 8 with a resistance value of 20 (kΩ) is connected, the distortion factor will be 5% as expressed by the following equation.

Further, as the on-resistance changes, the gain when outputting through the amplifier circuit also changes.

One way to solve this problem is to use P-channel MO.
3) There is a method of increasing the chip size of the transistor 1 and the N-channel MOS transistor 2 and changing the ratio of the chip sizes to reduce the on-resistance and reduce the distortion factor.

However, with this method, the distortion factor cannot be sufficiently reduced, and furthermore, the increased chip size makes it difficult to apply to integrated circuits.

On the other hand, as shown in FIG. 7, there is a method of setting the load resistance to a large value by connecting an operational amplifier circuit 10 having a voltage follower circuit configuration, but the stray capacitance 1
Due to the influence of 2, it is possible to avoid a drop in impedance on the high frequency side.
In this case as well, the distortion rate cannot be reduced sufficiently.

In other words, the stray capacitance 12 is C=5 (pF: l, the input signal S1 or S2 has a frequency of 20 (kHz), an amplitude level of ±2
Assuming a sine wave [■], the on-resistance of the switch circuits 4 and 6 changes by ±1 [kΩ] from the characteristic curve diagram in FIG.

Therefore, in this case, if the change in on-resistance is set as ΔR, then the distortion factor T1 is approximately expressed by the following formula:

On the other hand, as shown in FIG. 8, there is also a method of reducing the distortion factor using an operational amplifier circuit 14 having an inverting amplifier circuit configuration.

That is, the switch circuit 16 is inserted together with the feedback resistor Rf in the feedback path of the operational amplifier circuit 14, and the switch circuit 16 is
is kept on at all times.

Furthermore, the input resistors R1 and R have the same resistance value as the feedback resistor.
2, human input signals S1 and S2 are inputted, whereby changes in the on-resistance of the switch circuits 4 and 6 are corrected by changes in the on-resistance of the switch circuit 16.

According to this method, the distortion factor can be significantly reduced, but the input signals S1 and S2 are inverted and output, and the input impedance can be increased, and the resistance values of the input resistors R1 and R2 and the feedback resistor Rf There are disadvantages such as having to make them equal.

Therefore, in the case of this method, the method of use is limited, and there is a problem that it cannot be widely applied to analog circuits in general.

The present invention has been made in consideration of the above points, and aims to propose a switch circuit that can be applied to analog circuits in general and can significantly reduce distortion.

E Means for Solving the Problems In order to solve the problems, the present invention provides a first switch circuit section 4 (6) formed of a P-channel MOS transistor 1 and an N-channel MOS transistor 2.
), a second switch circuit section 24 formed of a P-channel MOS transistor 1 and an N-channel MO3I-transistor 2, and the first switch circuit section 4 (6). The output signal S
The operational amplifier circuit 22 is configured to feed back O to the inverting input terminal.

The input signal Sl is transmitted through the F-action first switch circuit section 4 (6).
(S2) is input to the non-inverting input terminal of the operational amplifier circuit 22, and the output signal SO of the operational amplifier circuit 22 is fed back to the inverting input terminal via the second switch circuit section 24.
The resistance value of the feedback resistor can be varied in response to a change in the on-resistance of the first switch circuit section 4 (6), so that it can be applied to general analog circuits to reduce distortion.

G example An embodiment of the present invention will be described in detail below with reference to the drawings.

In FIG. 1, in which parts corresponding to those in FIG. 8 are given the same reference numerals, 20 indicates a selection input circuit as a whole, forming an input circuit of an integrated signal processing circuit.

That is, the selection signals of the switch circuits 4 and 6 are input to the operational amplifier circuit 22 having a non-inverting amplifier circuit configuration, and the switch circuit 24 is inserted in the feedback path of the operational amplifier circuit 22.

In this state, the switch circuit 24 is always kept on.

Therefore, in the operational amplifier circuit 22, by maintaining a sufficient gain, the output signal SO is outputted so that the potentials of the non-inverting input terminal and the inverting input terminal are equal.

As a result, in the switch circuit 24, the on-resistance changes in accordance with the change in the on-resistance of the switch circuit 4 or 6, and the occurrence of distortion due to the change in the on-resistance of the switch circuit 4 or 6 can be significantly reduced. I can do it.

That is, if the signal levels of the human input signals S1 and S2 are set to 1, and the signal level of the output signal SO is set to vO, then using the gain A of the operational amplifier circuit 22 and the feedback factor F of the feedback circuit, the following relational expression is obtained. can be obtained.

However, let C be the stray capacitances 26 and 28 at the non-inverting input terminal and the inverting input terminal.

Here, since the on-resistance change ΔR of the switch circuit 4.6 is approximately proportional to the amplitude levels of the input signals St and S2, the on-resistance change ΔR2 of the switch circuit 24 is (3
), it can be expressed as the following equation.

Therefore, the distortion factor T2 of the selection input circuit 20 can be expressed by the following equation ■ jωC, which can be solved as jωC 1+AF −・TI (7), which results in the configuration shown in FIG. The distortion rate is approximately 1/A compared to
It can be seen that this can be reduced by a factor of two.

That is, even when using the operational amplifier circuit 22 with gain A=100, the distortion factor T2 can be reduced to 0.0006 (%).

In reality, the stray capacitances 26 and 28 depend on the shape of the wiring pattern, the layout of the switch circuit 4.6, etc.
They can be set to equal values within a practically sufficient range.

Furthermore, the gain A of the operational amplifier circuit 22 can also be set to a sufficiently high value.

Thus, in the selection input circuit 20 according to this embodiment, the distortion factor can be significantly reduced compared to the conventional one.

Furthermore, in switch circuit 4.6.22, the distortion factor can be reduced simply by setting the same cell size.
The cell size can be reduced, and the overall shape can be reduced by easily integrating the circuit.

Thus, in this embodiment, the switch circuits 4 and 6 constitute a first switch circuit section formed by the P-channel MO transistor 1 and the N-channel MOS transistor 2, respectively, whereas the switch circuit 24 similarly A second switch circuit section is formed of a P-channel MO3I-transistor 1 and an N-channel MOS transistor 2.

According to the above configuration, by inputting the selection signal of the switch circuit 4.6 to the non-inverting input terminal of the operational amplifier circuit 22 and feeding back the output signal of the operational amplifier circuit 22 through the switch circuit 24, The resistance value of the feedback circuit can be corrected following the change in the on-resistance of the switch circuit 4.6, thereby making it possible to significantly reduce the distortion factor compared to the conventional method.

In the above-described embodiment, the present invention was applied to a selection input circuit, but the present invention is not limited to this, and may be applied to switching an electronic volume 30 as shown in FIG. 2, for example. .

That is, in the electronic volume 30, the input signal S3
is divided by a series resistor circuit 32, and each divided voltage output is selected by switch circuits 33 to 37 and applied to the operational amplifier circuit 22.

As a result, the output signal level of the operational amplifier circuit 22 can be maintained at a signal level determined by the voltage division ratio of the series resistor circuit 32 and the selection inputs of the switch circuits 33 to 37. At this time, the switch circuit 24 turns on the switch circuits 33 to 37. By correcting resistance fluctuations, the distortion factor can be reduced significantly compared to the conventional method.

Further, in the above-described embodiment, a case has been described in which the switch circuit 24, which is a feedback circuit, is always kept on, but the present invention is not limited to this, and as shown in FIG. For example, the circuit 40 may be kept in an on state to constitute a variable gain amplifier circuit 42.

That is, in the variable gain amplifier circuit 42, the voltage dividing resistor 4
4 and 46 are switched, thereby switching the feedback factor of the operational amplifier circuit 22 and switching the overall amplification factor.

In such a variable gain amplifier circuit 42, by correcting variations in the on-resistance of the switch circuits 47 and 48 using the switch circuit 40, the distortion factor can be significantly reduced compared to the conventional one.

Furthermore, the present invention can be applied not only to the electronic volume 30 and the variable gain amplifier circuit 42, but also to switch circuits of various analog signal circuits to reduce the distortion factor.

Furthermore, in the above-described embodiments, the present invention is applied to a selection input circuit that is an integrated circuit, but the present invention is widely applicable not only to an integrated circuit but also to a case where the selection input circuit is configured using discrete components. can do.

H Effects of the Invention As described above, according to the present invention, a human input signal is input to the non-inverting input terminal of the operational amplifier circuit via the first switch circuit section, and a second input signal is input to the inverting input terminal of the operational amplifier circuit. By feeding back the output signal through the switch circuit section of the switch circuit section, fluctuations in the on-resistance of the first and second switch circuit sections can be mutually corrected, thereby reducing the distortion factor compared to the conventional switch. You can get the circuit.

5 is a characteristic curve diagram showing changes in on-resistance, FIG. 6 is a block diagram showing a selection circuit configured with the switch circuit, and FIGS. 7 and 8 are for explanation of distortion rate improvement. FIG.

1.2...MOS) transistor, 4.6.16
．． 24.33-37.40.47.48... Switch circuit, 10.22... Operational amplifier circuit.

Claims (1)

[Claims] P-channel MOS transistor and N-channel MO
A first switch circuit section formed of an S transistor, a P channel MOS transistor and an N channel MO
An input signal is inputted to the non-inverting input terminal via a second switch circuit section formed of an S transistor and the first switch circuit section, and an output signal is inputted via the second switch circuit section. A switch circuit comprising: an operational amplifier circuit that feeds back to an inverting input terminal.