Gain (output depends upon more than one input)

[riyaz.vlsi]

Hello frnds, I am involve in design of current mode analog circuit and working on TSMC0.18um process (cadence). Pls tell me how to find ac current gain, if output current depends upon two or three input signals.

 

[erikl]

1. Keep all DC input currents constant to attain a reasonable operating point
2. Attach a unit (1A) current source in parallel to the input from which you want to find the current gain
3. Run an ac analysis over your frequencies of interest
4. Plot the current gain (≙ output current) for this input. You can run this for every input.

 

[riyaz.vlsi]

1. Keep all DC input currents constant to attain a reasonable operating point
2. Attach a unit (1A) current source in parallel to the input from which you want to find the current gain
3. Run an ac analysis over your frequencies of interest
4. Plot the current gain (≙ output current) for this input. You can run this for every input.

Hello, the output current
Io= (I1 sC2+ gm I2- I3 (s^2 C1 C2 Rx+s C2+ gm ))/(s^2 C1 C2 Rx+sC2+gm )
is depend upon three inputs I1,I2,I3 simultaneously. when I1=I2=I3=I (let 1mA), the ac response implement high pass filter. my problem is that after applying ac simulation how to plot gain vs frequency curve as there are three inputs at a time. It gives wrong curve when i am clicking one of three inputs,pls resolve my problem.

 

[erikl]

plot the output current!

It gives wrong curve when i am clicking one of three inputs.

Of course. Read my advice thoroughly. Point 4.

 

[riyaz.vlsi]

Re: plot the output current!

Of course. Read my advice thoroughly. Point 4.

Thanks but I did not get correct response, might be i am doing something wrong.

 

[erikl]

Re: plot the output current!

I did not get correct response, might be i am doing something wrong.

How could we help you, if you don't communicate what you were trying, and which results you got?

 

[riyaz.vlsi]

Re: plot the output current!

How could we help you, if you don't communicate what you were trying, and which results you got?

Hello sir,
the output current is
Io= (I1 sC2+ gm I2- I3 (s^2 C1 C2 Rx+s C2+ gm ))/(s^2 C1 C2 Rx+sC2+gm ) and depends upon three inputs I1, I2, I3. its output current of current mode universal biquad filter. It implement different filter response for I1, I2, I3 value selections.
I1=Iin, I2=I3=0 (Band Pass filter)
I2=Iin, I1=I3=0 (Low " " )
I1=I2=I3=Iin (High " " )
I1=I3=Iin, I2=0 (Band reject filter)
I1=2Iin, I2=0, I3=Iin (All pass filter)
For Band pass and Low pass filter I got the correct frequency response (only one input rest are zero)
But for High pass, All pass and band reject filter, I got wrong frequency response (Here more than one input simultaneously), I am stuck and confused that at which input i must click to find gain response.

 

[erikl]

Re: plot the output current!

... which input i must click to find gain response.

We're turning in circles, sorry. It doesn't help if you repeat the same old info. Show your design, tell which simulator you're using, and tell us, why you think you have to click an input to find the gain response!

 

[riyaz.vlsi]

Re: plot the output current!

We're turning in circles, sorry. It doesn't help if you repeat the same old info. Show your design, tell which simulator you're using, and tell us, why you think you have to click an input to find the gain response!

Sorry, Actually I am using Cadence Virtuoso simulator.Normally I plot the gain by selecting output node first then input node in my simulator, that why i said which among three input i should select. Symbolic image of my design is attached:

https://obrazki.elektroda.pl/4621295700_1401128460.png

Ib1 & Ib2 are biasing current and Iin1, Iin2, Iin3 are input currents and Io output current, other information regarding filter selection are as i mention previouly.

 

[erikl]

So its probably the SPECTRE simulator. You didn't show your test bench nor tell which analysis you ran (ac, xf ?), nor if - and where - you added an ac current source input in order to measure the gain.

And I think you need a biquad specialist for your problem, not me, sorry.

 

[riyaz.vlsi]

So its probably the SPECTRE simulator. You didn't show your test bench nor tell which analysis you ran (ac, xf ?), nor if - and where - you added an ac current source input in order to measure the gain.

And I think you need a biquad specialist for your problem, not me, sorry.

Thanks, your advices helped me many times.