JPH0581364A - Simulation method for switched capacitor circuit - Google Patents

Abstract

(57) [Summary] [Object] The present invention relates to a method for simulating a switched capacitor circuit, and an object thereof is to be able to significantly reduce the operation time. [Structure] The variable resistor 1 has a resistance value inversely proportional to the frequency of a clock φ supplied to a switched capacitor, and is replaced with a switched capacitor for simulation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for simulating a switched capacitor circuit, and more particularly to a method for simulating a switched capacitor circuit.

[0002]

2. Description of the Related Art Conventionally, a switched capacitor has been known as a technique for forming a highly accurate resistor in an integrated circuit.

The switched capacitor is as shown in FIG.
A switch S1 provided between the input terminal 10 and the capacitor CO and a switch S2 provided between the capacitor CO and the output terminal 11 have clocks φ having the same frequency but opposite phases to each other.
* It is a configuration that switches by each φ.

[0004]

In the switched capacitor, the frequencies of the clocks φ and * φ are set sufficiently higher than the maximum frequency of the input signal at the input terminal 10. When simulating a switched capacitor with a computer, the input signal level is changed and the signal level of each of the connection point between the capacitor CO and the switches S1 and S2 and the output terminal 11 is calculated at a time interval shorter than at least the cycle of the clocks φ and * φ. ..

To simulate a switched capacitor, it is necessary to calculate the signal levels at a plurality of points at time intervals shorter than the clock cycle, so that there is a problem that a huge amount of calculation time is required.

The present invention has been made in view of the above points,
An object of the present invention is to provide a method for simulating a switched capacitor circuit that can significantly reduce the calculation time.

[0007]

1 and 2 show the principle of the method of the present invention.

In FIG. 1, the variable resistor 1 has a resistance value inversely proportional to the frequency of the clock φ supplied to the switched capacitor, and the variable capacitor 1 is replaced with the switched capacitor for simulation.

In FIG. 2, the frequency / voltage conversion circuit 2
Generates a control voltage whose level is inversely proportional to the frequency of the clock φ supplied to the switched capacitor.

The variable resistance value 3 has a resistance value proportional to the control voltage, and a simulation is performed by replacing the frequency / voltage conversion circuit 2 and the variable resistance 3 with a switched capacitor.

[0011]

In the present invention, since the switched capacitor which performs switching by the clock is replaced by the variable resistor 1, or the frequency / voltage conversion circuit 2 and the variable resistance circuit 3, the frequency sufficiently higher than the maximum frequency of the input signal during simulation. Irrespective of the clock, the simulation time interval is sufficiently shorter than the cycle of the highest frequency of the input signal, and the time interval can be made longer than in the past.

[0012]

FIG. 3 is a circuit diagram of a switched capacitor circuit, and FIG. 4 is a circuit diagram of an equivalent circuit to which the method of the present invention is applied.

In the switched capacitor circuit of the low pass filter shown in FIG. 3, the input terminal 20 is connected to the inverting input terminal of an operational amplifier (op amp) 22 via a switched capacitor 21.

The switched capacitor 21 has a clock φ.
Switch S1 for switching with and capacitor C1
And a switch S2 that inverts the clock φ and switches with the clock * φ. Operational amplifier 22
The non-inverting input terminal is grounded, the output terminal of the operational amplifier 22 is connected to the output terminal 23, and the switched capacitor 24 and the capacitor C3 are connected between the output terminal of the operational amplifier 22 and the inverting input terminal. Switched capacitor 2
4 is a switch S5 which is switched by the clock φ
And a switch S6 that is switched by the capacitor C2 and the clock * φ.

Here, the switched capacitors 21, 24
When the frequencies of the clocks φ and * φ are f and the capacitance of the capacitor C1 or C2 is C, each has a resistance value R represented by the following equation.

R = 1 / (Cf) (1) In FIG. 4, the switched capacitors 21 and 2 of FIG.
4 is replaced by variable resistors VR1 and VR2 of variable frequency type. The variable resistors VR1 and VR2 are supplied with the clock φ, and have variable resistance values according to the frequency f of the clock φ based on the equation (1).

In this embodiment, since the resistance values of the variable resistance values VR1 and VR2 can be determined by the frequency of the clock φ, the operational amplifier is sufficiently short in time interval than the cycle of the maximum frequency of the input signal coming into the terminal 20 during simulation. It suffices to calculate the signal level of each of the inverting input terminal 22 and the output terminal of 22, and this time interval may be longer than the clock cycle. As a result, the calculation time can be significantly shortened as compared with the conventional case.

FIG. 5 shows a circuit diagram of a second embodiment of an equivalent circuit to which the method of the present invention is applied. In FIG. 5, the switched capacitors of FIG. 3 are replaced by variable resistors VR3 and VR4 of variable voltage type.
And the control signals from the frequency / voltage conversion circuit 30 are supplied to the variable resistors VR3 and VR4, respectively.

The frequency / voltage conversion circuit 30 includes a monostable multivibrator (monomulti) 31, an integrating circuit 32, and
It is composed of an inverse circuit 33. The mono-multi 31 outputs the incoming clock φ as a predetermined pulse width, and the integrating circuit 32 integrates the clock of the predetermined pulse width to output a DC signal of a level substantially proportional to the frequency of the clock φ. The reciprocal circuit 33 generates a control signal Vf having a reciprocal level of the DC signal level. The control signal Vf is expressed by the following equation using the constant α.

Vf = α / f (2) Each of the variable resistors VR3 and VR4 has a resistance value R proportional to the control signal Vf as shown in the following equation.

R = βVf (3) where β is a proportional constant.

By setting αβ = 1 / C, the variable resistors VR3 and VR4 become equivalent to the switched capacitors 21 and 24 from the equation (1).

Here, the variable resistance V having the characteristic shown in the equation (3) is used.
There are N-channel MOS field effect transistors as R3 and VR4, and the variable resistors VR3 and VR4 in FIG. 5 can be replaced with MOS transistors Tr1 and Tr2 as shown in FIG.

In this embodiment, the simulation operation can be performed at a time interval sufficiently shorter than the cycle of the maximum frequency of the input signal, the operation time is shortened, and the monomulti 31, the integrating circuit 32, the reciprocal circuit 33, and the MOS are provided. The simulation can be performed using existing circuit elements such as the transistors Tr1 and Tr2.

[0025]

As described above, according to the method of simulating the switched capacitor circuit of the present invention, the time interval of the simulation operation can be made longer than before, and the operation time can be greatly shortened, which is extremely useful in practice.

[Brief description of drawings]

FIG. 1 is a principle diagram of the present invention.

FIG. 2 is a principle view of the present invention.

FIG. 3 is a circuit diagram of a switched capacitor circuit.

FIG. 4 is a circuit diagram of an equivalent circuit to which the method of the present invention is applied.

FIG. 5 is a circuit diagram of an equivalent circuit to which the method of the present invention is applied.

FIG. 6 is a circuit diagram of an equivalent circuit to which the method of the present invention is applied.

FIG. 7 is a circuit diagram of a switched capacitor.

[Explanation of symbols]

 1,3, VR1 to VR4 Variable resistance 2,30 Frequency / voltage conversion circuit 21,24 Switched capacitor 22 Operational amplifier

Claims (2)

[Claims] 1. A method for simulating a switched capacitor circuit for simulating a circuit using a switched capacitor, wherein the switched capacitor is replaced by a variable resistor whose resistance value is inversely proportional to the frequency of a clock supplied to the switched capacitor. A method for simulating a switched capacitor circuit, which is characterized by being performed. 2. A switched capacitor circuit simulation method for simulating a circuit using a switched capacitor, comprising: a frequency / voltage conversion circuit for generating a control voltage having a level inversely proportional to the frequency of a clock supplied to the switched capacitor; A method for simulating a switched capacitor circuit, characterized in that a simulation is performed by replacing the switched capacitor with a variable resistor whose resistance value is proportional to the control voltage.