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Design Languages >> Verilog-AMS >> 2nd order passive low pass filter
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Message started by ultimate on Feb 19^th, 2010, 10:35am

Title: 2nd order passive low pass filter
Post by ultimate on Feb 19^th, 2010, 10:35am

hello,

can somebody give me the verilog A code for 2nd order passive rc low pass filter(capacitors c1 c2 and resistor r)..

Title: Re: 2nd order passive low pass filter
Post by pancho_hideboo on Feb 19^th, 2010, 11:14pm

The followings are general notes for you.

- Always describe vendor's name and tool's name which you use.
- Don't do multiple posts which are same content.
- Don't request source code or behavioral model without any efforts.
- There are many simulators which have analyses called as PSS, PAC and Pnoise.
- Describe in detail with using correct terminologies.
- Warnigns are different from Errors.
- ADS is not name of simulator.
- There is no tool which name is Cadence.
- Don't use Direct Plot of Cadence ADE blindly without knowing definition.
- All gains in Direct Plot of Cadence ADE are "right", "true" and "practical" voltage gain.
- Don't mix up Simulation with Post Processing. They are completely different phase.
- MATLAB are different from Simulink.
- Learn measurements using actual instruments. Not "EDA Tool Play

ultimate wrote on Feb 19^th, 2010, 10:35am:

can somebody give me the verilog A code for 2nd order passive rc low pass filter(capacitors c1 c2 and resistor r)..

If you need physical modeling using R and C, you don't have to use Verilog-A.
And you can never generate complex poles if you use only R and C.

For behavioral modeling not physical modeling, what type of model do you need, bidirectional or unidirectional ?
Do you need input and output impedance ?
Is your requirement enough with signal flow model ?

For example, if we use S-parameter formulation, there are three options at least.

(1) Model expressing only S21.
(2) Model expressing {S11, S21, S22}.
(3) Model expressing {S11, S12, S21, S22}, that is, full model.

(1) and (2) are unidirectional.
(3) is bidirectional.

Title: Re: 2nd order passive low pass filter
Post by Marq Kole on Mar 2^nd, 2010, 6:15am

If you want a model, here it is; for the rest I agree completely with Pancho.

`include "disciplines.vams" module lpf(in, out, gnd); parameter real c1 = 100p from [0:inf); parameter real r1 = 10k from [0:inf); parameter real c2 = 1p from [0:inf); inout in, out, gnd; electrical in, out, gnd; electrical n1; analog begin I(n1, gnd) <+ c1 * ddt(V(n1, gnd)); V(in, n1) <+ r1 * I(in, n1); I(in, gnd) <+ c2 * ddt(V(in, gnd)); V(in, out) <+ 0; end endmodule

Title: Re: 2nd order passive low pass filter
Post by pancho_hideboo on Mar 2^nd, 2010, 6:47am

Marq Kole wrote on Mar 2^nd, 2010, 6:15am:

analog begin
I(n1, gnd) <+ c1 * ddt(V(n1, gnd));
V(in, n1) <+ r1 * I(in, n1);
I(in, gnd) <+ c2 * ddt(V(in, gnd));
V(in, out) <+ 0;
end

???????
What LPF do you want to realize ?

Don't you have typo for "V(n1, out) <+ 0;"

I think it should be :
Quote:

module lpf(in, out, ref);

parameter real r1 = 10k from [0:inf);
parameter real c1 = 100p from [0:inf);
parameter real r2 = 1k from [0:inf);
parameter real c2 = 1p from [0:inf);

inout in, out, ref;
voltage in, out, ref;

electrical n1, n2, n3, n4;

analog begin
V(n1) <+ V(in, ref);

V(n1, n2) <+ r1 * I(n1, n2);
I(n2) <+ c1 * ddt(V(n2));

V(n3) <+ V(n2);

V(n3, n4) <+ r2 * I(n3, n4);
I(n4) <+ c2 * ddt(V(n4));

V(out, ref) <+ V(n4);
end

endmodule

This is "Signal Flow Model" for second order RC LPF.

Title: Re: 2nd order passive low pass filter
Post by Marq Kole on Mar 2^nd, 2010, 7:21am

Hi Pancho,

This is not signal flow, this is current input, voltage output, the kind of model you would use in a simple PLL. The input is attached to the charge pump which delivers a current, while the output is connected to the VCO which requires a voltage. If you read the specifications there was a specific request for c1, c2 and r - then I guessed this was kind-of the application needed for this filter which I had laying around anyway.

Cheers,
Marq

Title: Re: 2nd order passive low pass filter
Post by pancho_hideboo on Mar 2^nd, 2010, 7:26am

Marq Kole wrote on Mar 2^nd, 2010, 7:21am:

the kind of model you would use in a simple PLL.

I got.

Title: Re: 2nd order passive low pass filter
Post by zahrein on Nov 9^th, 2011, 9:32pm

Quote:

May i know the "ref" refer to what output from the p/f detector?

Title: Re: 2nd order passive low pass filter
Post by Marq Kole on Nov 13^th, 2011, 1:27pm

ref = signal ground.

In most applications it will be connected to the vss, gnd, or whatever is your reference signal level.

Cheers,
Marq

Title: Re: 2nd order passive low pass filter
Post by zahrein on Nov 13^th, 2011, 5:18pm

i see thanks for the info.