Switched capacitor integrator simulation dating

How to simulate a switched capacitor circuit?

switched capacitor integrator simulation dating

A comparator-based switched-capacitor (CBSC) integrator is presented. In contrast to an A new charge control circuit is proposed to control the charge transfer phase of a CBSC integrator. Date Added to IEEE Xplore: 10 October Join Date: Mar ; Location: GREECE; Posts: 71; Helped: 2 / 2; Points: 1,; Level: 10 how to simulate switched capacitor circuits. 86 | Page. Optimized Design of Switched-Capacitor (SC) Integrator Date Of Submission: from the equivalent switched capacitor circuit and in.

Low-Voltage Fully Differential CMOS Switched-Capacitor Amplifiers

For those of you who are new to Micro-Cap, take our features tour to see what Micro-Cap has to offer. This article will explain a little of the theory and show how to run simulations on these circuits. Theory Consider the simple low pass SC filter and its equivalent analog filter circuit shown below.

When S1 is closed, the capacitor C1 charges to VA. Then S1 opens and C1 holds the charge and voltage.

switched capacitor integrator simulation dating

The change in charge on C1 is Qinitial - Qfinal. Switched capacitors behave like resistors: They can easily create large-valued resistances, which is otherwise very hard to do in integrated circuits. Resistances larger than 1E6 are easy to create. Precise control of F0: Both the frequency and the ratio can be controlled very precisely better than. Since this is far superior to what can be achieved with the absolute value of resistors or capacitors, it is a key consideration in using SC filters.

Here is the transient analysis of the circuit and its Fourier spectrum: The bottom plot on the left shows the output of the SC blue and analog green filters superimposed.

The spectrum plot on the right shows the dominant component at 1kHz is There are other frequencies as well. In this case, the unwanted frequencies are at 19kHz, 21kHz, 39kHz, 41kHz, and so on. If these are a problem in the design, they can easily be removed with a simple, low tolerance analog filter.

It may seem odd to have to use an analog filter to 'cleanup' after a messy SC filter, but doing so is cheap and easy and still yields a filter with precision control of its band characteristics.

switched capacitor integrator simulation dating

In this circuit we've built a conventional analog lossy integrator and its SC equivalent. The SC integrator is built in the same way as its analog cousin but with the resistor replaced with the equivalent SC resistor. This makes the integrator function in the same way as its analog counterpart. This type of ideal switch exhibits no overlap or nonlinearities. Here is a transient analysis plot showing both analog and SC waveforms overlaid. Integrators can be used to build band pass filters as in this example.

But, help is on the way!

Simulating Switched Capacitor Filters - Winter

By slightly modifying the way the capacitor is switched, the simulated resistor becomes immune to the surrounding strays. One end connects to the input voltage; the other feeds into the virtual ground of an op amp.

Virtual ground simply means that the op amp works to keep its negative input near ground, so the input ends up looking like a low impedance node at 0V.


The operation is straight forward. Switches S1A and S1B are alternately closed and opened. With S1A closed, C1 charges up to Vin. Alternately, with S1B closed, C1 discharges into the virtual ground to 0V.

switched capacitor integrator simulation dating

But, where does this charge go? Because no current flows into the op amp, C2 receives the charge! What kind of waveform can we expect at the output?

  • Switched capacitor

A bipolar square wave at the integrator's input should generate a triangle wave at its output. First, let's see the standard integrator circuit in action by plotting V 6. Okay, now let's look at the switched-cap integrator at V 4. Hey, check it out - the waveform is the same almost! The only difference is that the switched-cap output rises in a stair-stepped waveform.

switched capacitor integrator simulation dating

The input current gets delivered in spikes as S1B is repeatedly opened and closed. But on average, the same current flows into C2 as in the standard integrator. Just remember to calculate the equivalent resistor for R2 if you want to compare the two integrators.