JPS60103806A - Amplifier circuit - Google Patents

Abstract

PURPOSE:To attain amplification without noise component by providing a filter circuit stopping a frequency of a control signal to one end of a feedback circuit having an SCF (switched capacitor filter) so as to block the feedback of a leakage signal in synchronizing with the control signal of the SCF. CONSTITUTION:An input signal Vin is applied to a non-inverting input terminal (+) of an operational amplifier 1. The amplification factor and the frequency characteristic are decided by two switched capacitor filters (SCF) 2, 3 constituting a feedback circuit. While the SCF1 makes circuit operation, an output signal Vout is leaked via a stray capacitor C0. The supply of said leakage signal to the inverting input terminal (-) is blocked in said amplifier circuit. That is, a resistor R2 and a capacitor C2 constitute a low-pass filter 4. The cut-off frequency is set to a frequency lower than the frequency of the control signal. The leakage signal is synchronized with the frequency of the control signal. Thus, the leakage signal is blocked by said low-pass filter 4 and is not applied to te inverting input terminal (-).

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to an amplifier circuit suitable for use in each persimmon audio device.

[Background technology]

The present inventor has developed a technique that uses a switched capacitor filter (hereinafter referred to as 8CP9) in the feedback circuit of a feedback amplifier circuit.

Prior to the invention of the present application, the present inventor further conducted various technical studies regarding the amplifier circuit. As a result, it was found that the following defects were present.

That is, to drive the SCF, a clock pulse of frequency f is supplied as a control signal.

The control signal turns the switch element on and off, but since the switch element has stray capacitance, signal leakage occurs in synchronization with the clock pulse. The inventor's studies have revealed that if this leakage signal is fed back as it is, a phase-inverted and amplified leakage signal will appear at the output end of the amplifier circuit.

[Purpose of the invention]

An object of the present invention is to provide an amplifier circuit that can prevent clock pulses from leaking from the SCF.

The above and other objects and novel features of the present invention will become apparent from the description of the present specification and the accompanying drawings.

[Summary of the invention]

A brief explanation of the gold dust of the invention disclosed in this application is as follows.

In other words, a filter circuit for blocking the frequency f of the control signal is provided at one end of the feedback circuit having the SCF, and the leakage signal synchronized with the control signal of the 8CF is prevented from being fed back, thereby performing amplification without noise components. It achieves the purpose of the invention.

[Embodiment 1] Hereinafter, a first embodiment of an amplifier circuit to which the present invention is applied will be described with reference to FIG.

An input signal ■in is supplied to the positive phase input terminal of the operational amplifier 1. Then, the output signal V is applied to the output terminal of the operational amplifier 1.
Out is obtained, and its amplification degree and frequency characteristics are determined by two switched capacitor filters (hereinafter referred to as 8CF) 2.3 forming a feedback circuit.

The SCF is already known among those skilled in the art, but its outline is as follows.
When the switch Q is on, the output (No. 8 V
out is charged to the capacitor CA. Then, when the phase of the control signal φ2M is reversed, the switch Q is turned off and the switch Q2 is turned on. As a result,
The charge stored in the capacitor CA is discharged via the switch Q.

Therefore, in 80F1, the amount of signal transmission is the capacitor C
It is determined by the capacitance C of A, the control signal φ, and the frequency f of 7. Therefore, if the entire 5CF2 is regarded as one resistor R6, R,=3.

For 5CF3, the same circuit operation as for 5CFI is performed. 5CFI,2 are driven by a common control signal φ,7, so if CA=CB, R
, -=R, holds true. Capacitor C1 is for direct current blocking. Therefore, R,=R.

Then, a voltage divided by resistors R0, R, will be generated at point A, and the voltage division ratio will be determined by capacitors CA, C.
Determined by B.

By the way, although the switches Q, Q2 are constructed of PET, a stray capacity C6 is interposed between each gate and source. Therefore, while 8CF1 is performing the circuit operation, the output signal Vout leaks through the stray capacitor C8. However, this leakage does not occur continuously, but occurs when the control signal φ undergoes 70 phase inversions. Therefore, the leakage signal (not shown) is proportional to the frequency f of the control signals φ and V. If the return 1i voltage containing the leakage signal is supplied as it is to the negative phase input terminal -, the leakage signal will be amplified in negative phase and will appear at the output terminal.

However, in the amplifier circuit to which the present invention is applied, the leakage signal is prevented from being supplied to the negative phase input terminal.

That is, the resistor R21 and the capacitor C7 constitute the low pass filter 4. Its cutoff frequency is the control signal φ
, 7 is set to a lower frequency than the frequency f. The leakage signal is synchronized with the control signal φ and the 70 frequency 'Af, as described above. Therefore, the leakage signal is blocked by the low-pass filter 4 and is not supplied to the negative phase input terminal. Therefore, the feedback voltage VA of the output signal Out is supplied to the negative phase input terminal -, and the output signal Vout is obtained by voltage comparison between the feedback voltage VA and the input signal Vin. Leakage No. 48 does not appear in the output signal Vout.

[Embodiment 2] Next, a second embodiment of the present invention will be described with reference to FIG. The differences between this example and the first example are as follows:
Instead of the low-pass filter 4, an FBTQ++ is provided. Therefore, for convenience of explanation, the same parts as in the first embodiment are given the same reference numerals, and the explanation thereof will be omitted.

A capacitor C8 as described above is interposed between the gate and source of FETQo. The drain of FETQ++ is placed in a floating state, and the control signal M is supplied to the gate.

When 5CF2 operates as described above, a leakage signal appears at point A. However, when the leakage signal appears, F
The gate of B T Q++ is brought to a low level by the control signal 7, so to speak, as if it were grounded. Therefore,
The leakage signal appearing at point A is absorbed by the gate circuit.

As a modification of this embodiment, a capacitor Cx may be connected to the train of FETQn as shown by a dotted line, and one end of the capacitor Cx may be grounded by the control signal φ. In this case, when the phase of the control signal φ is inverted, FBTQ+t is turned on, and the leakage signal appearing at point A is
+, absorbed through capacitor Cx. Capacitor C
X may have a small capacitance, and a junction capacitor formed within the IC can be used.

〔effect〕

<1) By providing a noise canceller in the feedback loop of the operational amplifier and preventing feedback of the leakage signal that has been rotated to the control signal of the SCF, it is possible to obtain the effect of removing the noise component of the signal that has not been amplified.

[Application field]

The present invention can be applied to at least a feedback type amplifier regardless of whether it is used for audio or high frequency.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of an amplifier circuit to which the present invention is applied. FIG. 2 is a circuit diagram showing another embodiment of the amplifier circuit to which the present invention is applied. 1... Amplifier, 2, 3... SCF, 4... Filter circuit, cl p C2p CA + CB = Core f 7S, <6° 1... Control signal, VA... Feedback voltage , Ql r Qt + QR+Q4 r Q++...
・Switch element, ■9...Feedback voltage. Agent Patent Attorney Akira Takahashi Ravi...1...

Claims (1)

[Claims] 1. The switched capacitor filter is connected to one end of the feedback circuit having at least a switched capacitor filter.
An amplifier circuit characterized in that a filter circuit different from the filter is provided, and the filter circuit removes noise components generated in the switched capacitor filter.