JPH01265710A - Switched capacitor type automatic variable resistor circuit - Google Patents

Abstract

PURPOSE:To form a small-sized automatic variable resistor circuit with high accuracy by varying the frequency divider ratio of two variable frequency dividers of a capacitor type amplifier circuit. CONSTITUTION:The circuit consists of an oscillator 1 whose oscillating frequency is f0, variable frequency dividers 2, 3 frequency-dividing said frequency f0 into 1/M and 1/N respectively, switched capacitor circuits 4, 5 and an operational amplifier 6, the signal level from an input terminal 10 is varied and outputted from an output terminal 11. The frequency divider ratio of the variable frequency dividers 2, 3 is varied to vary the gain. Since the gain is decided by the frequency divider ratio, the small-sized automatic variable resistor circuit with high accuracy is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an autovolume circuit composed of a switched capacitor circuit.

[Conventional technology]

Conventionally, the capacitance of the input capacitor is determined by the capacitance value of the input capacitor and the capacitor in the feedback path of the operational amplifier (hereinafter referred to as the operational amplifier). A common circuit is to obtain a desired capacitance ratio by changing the filter gain to a desired value.

[Problem to be solved by the invention]

The conventional switched capacitor type OI volume circuits mentioned in 1 to 1 above require capacitors depending on the variable width and variable number of the O1 heporium, and when this circuit is integrated on an MO8 type integrated circuit, the chip size becomes large. It has the disadvantage of becoming. In particular, even if the degree of integration increases with MO3 type integrated circuits, the size of the switch will become smaller, but the capacitor needs to have higher specific accuracy, and the capacitance value is large enough that stray capacitance such as parasitic capacitance is not a problem. There was a certain necessity, and the transistors that made up the sophisticated operational amplifier had the disadvantage that they could not be made smaller due to noise and ratio accuracy problems.

An object of the present invention is to eliminate these drawbacks and provide an autovolume circuit that can be formed with high accuracy and in a small area by determining the gain by the frequency division ratio.

[Means to solve the problem]

The configuration of the present invention is such that two circuits each having a switch provided between each electrode of a capacitor, a connecting terminal, and ground are connected in parallel, and a switch 1 and a capacitor circuit are connected between an input terminal and an input/output terminal of an operational amplifier, respectively. The switched capacitor type autovolume circuit provided includes variable frequency dividing means for respectively varying the clock frequency for opening and closing each switch of the two switched capacitor circuits, and by varying the frequency dividing ratio of these variable frequency dividing means. It is characterized by variable gain.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

FIGS. 1(a) and 1(b) are a circuit diagram and its waveform diagram showing an embodiment of the present invention. In this embodiment, the oscillation frequency fo
oscillator] and this frequency fo is 1/M, ], /N
It is comprised of a variable frequency divider 2.3, switched capacitor circuits 4 and 5, and an operational amplifier 6, which varies the signal level from the input terminal 1.0 and outputs it from the output terminal 1.

switch SN of the switched capacitor circuit 4 on the input side,
is opened and closed by a clock φN1 whose frequency is divided by 1/N, and the switch SN2 is opened and closed by a clock φN2. Also, switch L on the feedback side - switch S of the capacitor circuit 5
N2 is opened and closed by clock φold, and switch SM□ is opened and closed by clock φM2. Capacitor C1 and capacitor C2 on the input side have the same capacitance value, and capacitor C3 and capacitor C4 on the feedback side have the same capacitance value.

Now, assuming that Cl=C2=CR1, C3=C4=CR2, each circuit 4, 5 has the following resistance value isometrically.

Here, fo is the clock frequency of oscillator 1, N, M
is the frequency division number of each variable frequency divider 2, 3.

As shown in the figure, when the clock φM1 is "high" and the clock φM2 is "low", the switch SMI is closed and the switch SM2 is open, but at this time, the capacitor C3 becomes the negative feedback path of the operational amplifier. Conversely, when the clock φM1 is “low” and the clock φ8□ is “high”, the switch SM□ is open and the switch SM2 is closed, and at this time, the capacitor C4 becomes the negative feedback path of the operational amplifier.

In this case, the gap (slit) between the clock φM1 and the clock φM2 can be made sufficiently short with respect to the settling time of the operational amplifier 6, so the time during which the input and output of the operational amplifier 6 are simultaneously disconnected can be shortened, and therefore the output of the operational amplifier 6 is It remains constant without saturating and operates normally.
In other words, the circuit function of an anti-phase amplifier can be obtained. At this time, the gain of the anti-phase amplifier is as follows.

G=R2/R,...(3) From equations (1) and (2), the following equation can be obtained.

Here, since CR1/CR2 are constant values, if the frequency division ratios M and N are varied, the gain G can be varied, and the circuit can be configured with an autovolume.

As can be seen from the figure, since the configuration of the switched capacitor circuit is a parasitic capacitance-insensitive circuit, the gain shown by equation (4) is accurately determined by the ratio of the respective frequency division ratios M and H, and the autovolume Each step width can be obtained with extremely high accuracy.

Further, on the MO8 type integrated circuit, the variable frequency divider can be easily realized with a smaller chip area than an operational amplifier.

[Effects of the Invention] As explained above, the present invention has the advantage that a volume circuit can be configured by varying the frequency division ratio of two variable frequency dividers of a switched capacitor type amplifier circuit.

[Brief explanation of the drawing]

FIGS. 1(a) and 1(b) are a circuit diagram and its waveform diagram showing an embodiment of the present invention. ]...Oscillator, 2, 3...Variable frequency divider, 4, 5
...Circuit network, 6...Operation amplifier, 10...Input terminal, 1]...Output terminal, SNI, SN1. SMI
, 3M2...switch, CI, C2, CB, C4
...Capacitor.

Claims (1)

[Claims] A switched capacitor type autovolume in which two switched capacitor circuits each having a switch connected between each electrode of the capacitor, a connection terminal, and ground are connected in parallel between the input terminal and the input output terminal of an operational amplifier. The circuit is characterized by comprising variable frequency dividing means for respectively varying the clock frequency for opening and closing each switch of the two switched capacitor circuits, and for varying the gain by varying the dividing ratio of these variable frequency dividing means. Switched capacitor type autovolume circuit.