simple swtiched capacitor circuit using macro op apm model

[mahyar]

simple capacitor circuit

Hi
i am trying to simulate a very basic switched capacitor circuit in Virtuoso using a macro op apm model. But when i simulate, as you see in the picture

https://obrazki.elektroda.pl/70_1243607809.jpg

in DC analysis there is very big offset in the output.
and in transient analysis there is an error: no DC convergence
I think my problem is the op amp variables that i have to set up correctly but i don't know if I am right.
my input sin wave has a freq. of 1 KHz
my switches are sampling with f = 4 KHz.
op amp variables:
open loop gain: 10000
GBW: 160 MHZ
negative supply current: 100u
positive supply current: 100 u
out put voltage swing: +- 1.2
nominal supply voltage: 1.2

 

[LvW]

simple op amp circuits with capacitors

I am not familiar with Virtuoso.
Nevertheless. two comments are to be made:

1.) The circuit cannot work with singel supply as you have no unity gain feedback for dc. That means there is no operating point in the linear region for the opamp .

2.) What do you expect from a dc analysis of a time variant (clocked) circuit ?

 

[mahyar]

simple capacitor circuits

thank you
1- but what should i do to make it works?
2- By the dc analysis I just want to check the output offset at the op-amp that should be reasonable at any time sample.

 

[LvW]

op apm

thank you
1- but what should i do to make it works?
2- By the dc analysis I just want to check the output offset at the op-amp that should be reasonable at any time sample.

1.) Use split power supply. That´s normal for S/C circuits.
2.) Of course, dc analysis doesn´t work for sampled data systems. Instead, you must use tran analysis.

 

[mahyar]

advertisements index page/apm models

Even when I use the separate power supplies (+1.2v & -1.2 v) it has the same problem. I understand what you mean and it doesn't really make sense to use DC analysis for the clocked circuits and I do the trans. analysis as well but yet in the DC analysis I shouldn't see the 959V at my output and that's the reason I don't have my proper output in the trans. as well.

 

[LvW]

Re: simple swtiched capacitor circuit using macro op apm mod

.....................
959V

???

 

[mahyar]

Re: simple swtiched capacitor circuit using macro op apm mod

yes if you see my attached figure it has a very big output voltage:

https://obrazki.elektroda.pl/70_1243607809.jpg

 

[LvW]

Re: simple swtiched capacitor circuit using macro op apm mod

yes if you see my attached figure it has a very big output voltage:

https://obrazki.elektroda.pl/70_1243607809.jpg

Perhaps it would be wise to think if this voltage is a reasonable value.
From where does it originate ?

 

[Cesar92]

Re: simple swtiched capacitor circuit using macro op apm mod

.....................
959V

???

so the origine of your 998.5V come from your not inverter input amplifier:
you have: V+=998,5V mybe (V+=998,5mV) and not 998,5V.