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Simulators >> RF Simulators >> time variant impedence in a passive mixer
https://designers-guide.org/forum/YaBB.pl?num=1240334878

Message started by macg84 on Apr 21^st, 2009, 10:27am

Title: time variant impedence in a passive mixer
Post by macg84 on Apr 21^st, 2009, 10:27am

Hello,

In the attached file there is a double balanced passive mixer, i read thet this mixe with a passive filter in the output it work in turn as a fileter. To verify this condidtion I have to evaluate the impedence at the input of this mixer (how you can see in the attachet file). but This impedence is time variant, how can I do to evaluate this impedence??
Thank you

Title: Re: time variant impedance in a passive mixer
Post by pancho_hideboo on Apr 21^st, 2009, 10:44am

macg84 wrote on Apr 21^st, 2009, 10:27am:

To verify this condidtion I have to evaluate the impedence at the input of this mixer (how you can see in the attachet file). but This impedence is time variant, how can I do to evaluate this impedence??

You can evaluate impedance averaged over one period of Local signal by invoking master steady state analysis using one tone large signal followed by slave small signal analysis.

If you use Agilent ADSsim(RFDE), use 1tone-HB-SS Analysis.
If you use Agilent GoldenGate, use 1tone-SSNA Analysis.
If you use Cadence Spectre, use PSS/PAC Analysis.

Title: Re: time variant impedence in a passive mixer
Post by macg84 on Apr 21^st, 2009, 11:00am

Thank you,

I cn use PSS+PAC analysis, but I have some question about this. To evaluate the time invariant inpedence. In the input port how do i have set "Source type"? Do i have ti set "PAC magnitude" equal to 1?
In PSS analyses how can choose the beat frequency? And the number of harmonics?
And in PAC analyses how can choose the MAXIMUM sideband?

Thank youuuuuuuuuuuu very much

Title: Re: time variant impedance in a passive mixer
Post by pancho_hideboo on Apr 21^st, 2009, 11:05am

macg84 wrote on Apr 21^st, 2009, 11:00am:

In the input port how do i have set "Source type"? Do i have ti set "PAC magnitude" equal to 1?

"Source type=dc", any nonzero value for "PAC magnitude".

macg84 wrote on Apr 21^st, 2009, 11:00am:

In PSS analyses how can choose the beat frequency?
And the number of harmonics?
And in PAC analyses how can choose the MAXIMUM sideband?

There is no beat frequency in PSS of Cadence Spectre.
http://www.designers-guide.org/Forum/YaBB.pl?num=1232036048/4#4

"fund for pss" is Frequency of Local Signal.
"harms for pss" and "maxsideband for pac" are depend on your needs.

Title: Re: time variant impedence in a passive mixer
Post by macg84 on Apr 22^nd, 2009, 2:26am

Ok thank you, but I have another quastion sorry...after the pss and pac analyses I can plot corrent and voltage, but I want print the impedence, hence V/I, I thought to use calculator to make this, using the comand Vf and If , but I don't get any results.
How can I do??

Thank youuuuuu very much

Title: Re: time variant impedance in a passive mixer
Post by pancho_hideboo on Apr 22^nd, 2009, 6:00am

macg84 wrote on Apr 22^nd, 2009, 2:26am:

but I want print the impedence, hence V/I, I thought to use calculator to make this, using the comand Vf and If,
but I don't get any results.

You don't seem to understand Cadence ADE and Spectre.

vf and if of Calculator are for conventional AC analysis not for PAC analysis.

Use Direct Plot for PAC with "Add To Outputs" enabled.
Then modify "Expression" in "Setting Outputs".

You can also choose following methods.
- Use Results Browser with Calculator for selecting PAC results and processing some math operations.
- Write Ocean Script.

Your questions are no more than simple usage of very specific EDA vendor's tool.
Read documentations surely.

Title: Re: time variant impedence in a passive mixer
Post by macg84 on Apr 22^nd, 2009, 9:31am

Thank youuuuu... I used results browser and saw how it works on cadence cadence documentation, but in this documentation does not explain that when i choose e current node there is four choose (PLUS,n,ns,ps) what is you meaning?

Where can I find information about other ways to evaluate the impedance?

Thank youuuuuuuuuuuuuuuuuuuuuuuuuuuu

Title: Re: time variant impedance in a passive mixer
Post by pancho_hideboo on Apr 23^rd, 2009, 6:48am

It seems you could not understand the following. This is most easy method.

pancho_hideboo wrote on Apr 22^nd, 2009, 6:00am:

Use Direct Plot for PAC with "Add To Outputs" enabled.
Then modify "Expression" in "Setting Outputs".

macg84 wrote on Apr 22^nd, 2009, 9:31am:

I used results browser and saw how it works on cadence cadence documentation, but in this documentation does not explain that

I can't understand meaning of your sentence. What do you mean ? What do refer by "this" and "that" ? :-/

macg84 wrote on Apr 22^nd, 2009, 9:31am:

when i choose e current node there is four choose (PLUS,n,ns,ps) what is you meaning?

I can't understand meaning of your sentence. :-/
There is no current in node. Node is different from terminal.
Maybe an instance you choose in result browser has four terminals, (PLUS,n,ns,ps), although I can't understand meaning of your sentences.

macg84 wrote on Apr 22^nd, 2009, 9:31am:

Where can I find information about other ways to evaluate the impedance?

Do you surely read documenations ? :-?

http://www.designers-guide.org/Forum/YaBB.pl?num=1237293628
http://www.designers-guide.org/Forum/YaBB.pl?num=1237382945/6#6

Title: Re: time variant impedence in a passive mixer
Post by aaron_do on Apr 23^rd, 2009, 7:29pm

Hi,

for cadence spectre, the way I normally check the input impedance of a passive mixer would be to run PSS/PSP analysis. You can then plot the Z parameters or the Y parameters of the input port.

cheers,
Aaron

Title: Re: time variant impedence in a passive mixer
Post by Ken Kundert on Apr 23^rd, 2009, 11:47pm

You know, SpectreRF does not require the use of ports as sources. You can use either voltage sources or current sources too.

In addition, you might want to check out http://www.designers-guide.org/Analysis/diff.pdf for more flexible approach to building a testbench for differential circuits.

-Ken

Title: Re: time variant impedance in a passive mixer
Post by pancho_hideboo on Apr 24^th, 2009, 4:23am

aaron_do wrote on Apr 23^rd, 2009, 7:29pm:

for cadence spectre, the way I normally check the input impedance of a passive mixer would be to run PSS/PSP analysis.
You can then plot the Z parameters or the Y parameters of the input port.

If you use PSP or QPSP of Cadence Spectre, you have to use "analogLib/port" which results in load at observation nodes.

Such loads at observation nodes are not preferable especially for interstage impedances measurements.
Here even if you increase port resistance, it can not be a solution.

I use my own impedance probe. For example, the following is single-ended impedance probe.
http://www.designers-guide.org/Forum/YaBB.pl?num=1221012939

In Agilent ADSsim, such impedance probe(Short_Probe or SP_Probe) is provided as standard probe.
http://edocs.soco.agilent.com/display/ads2009/SP+Probe+%28S-Parameter+Probe%29
But I can't use this ADSsim's probe in Cadence Spectre.
And this probe is restricted to only conventional SP-Analysis.

Instead I created my own impedance probe by using vsources, isources and ideal-transformer.
This impedance probe is valid not only for Agilent RFDE(ADSsim) but also for Cadence Spectre.
And this impedance probe is valid not only for conventional Small Signal AC Analysis but also for Small Signal AC Analysis subjected to Master Large Signal Analysis such as HB-SS of Agilent RFDE(ADSsim) and PSS/PAC of Cadence Spectre.

Assume cascaded connections of LNA, Mixer, Filter and IF_Amp, etc.
How do you measure any interstage impedances which see left and right ?

I can measure any interstage impedances using my own differential impedance probe.
Here I can evaluate Zleft_diff, Zleft_comm, Zright_diff and Zright_comm of any interstage at same time.

Ken Kundert wrote on Apr 23^rd, 2009, 11:47pm:

You know, SpectreRF does not require the use of ports as sources. You can use either voltage sources or current sources too.

We all know any vendor's RF simulator except for very old one such as "SuperCOMPACT" does not require the use of ports as sources.

Title: Re: time variant impedence in a passive mixer
Post by macg84 on Apr 24^th, 2009, 7:13am

Thank you all for your suggestions... ;)

This circuit represent a mixer filter, a band pass filter whose corner frequency are Flo+Frc and Flo - Frc, where Flo= is the local oscillator frequency while Frc= is the corner frequency of the two low-pass filter placed Outgoing the mixer.
I use the analysis PSS + PAC and then try to evaluate the voltage and current from the point 1, do not get anything, if I go to evaluate the node 2 get values, but I think that is not the correct analysis in this way.
I used lanalisi PSS + PSP and I went to select "direct plot form" PSP analyses and ZP, to measure the Z11 ipedence input. Also in this cases do not get good values, but really sneezing.:'(

How can I do??????

Title: Re: time variant impedence in a passive mixer
Post by macg84 on Apr 24^th, 2009, 7:41am

In the circuit, I replaced Nmos with ideal switches, so that i can neglect the problem due to design these.

Help me please please, I do not know how to go on ...

Title: Re: time variant impedance in a passive mixer
Post by pancho_hideboo on Apr 24^th, 2009, 8:10am

macg84 wrote on Apr 24^th, 2009, 7:13am:

I use the analysis PSS + PAC and then try to evaluate the voltage and current from the point 1, do not get anything,

Why do you evaluate voltage and current at point 1 ?

macg84 wrote on Apr 24^th, 2009, 7:13am:

I used lanalisi PSS + PSP and I went to select "direct plot form" PSP analyses and ZP, to measure the Z11 ipedence input.
Also in this cases do not get good values, but really sneezing.:'(

What is "lanalisi" ?
S11, S12 and S22 of PSP results using your schematic have no meaning.
Only S21 might has some meaning value.
On the other hand, {Z11, Z12, Z21, Z22} and {Y11, Y12, Y21, Y22} have no meaning completely.

macg84 wrote on Apr 24^th, 2009, 7:41am:

In the circuit, I replaced Nmos with ideal switches, so that i can neglect the problem due to design these.

Even if they are NMOS, there is no problem. Your problem exist in other.
First, usage of signal sources.
Second, setting of analysis.
Third, measuring impedance.

There are too many misunderstandings in your schematic regarding basic circuit theory you have.
So it is very laborious to correct all.

I'm not kind and patient enough for explaining such too basic issues.
Maybe other people who are kind hearted and very patient will help you.

Title: Re: time variant impedence in a passive mixer
Post by macg84 on Apr 24^th, 2009, 8:27am

Sorry, Where can I find the useful material to learn??

However thank you very much for the other advice

Title: Re: time variant impedence in a passive mixer
Post by aaron_do on Apr 24^th, 2009, 10:21pm

Hi pancho_hideboo,

Quote:

I was thinking that we can leave the output open circuit (or whatever the desired load is), and use a port at the RF input. Is this setup ok for measuring Z11?

Also, I was thinking that the LO leakage to either RF or IF ports can affect the operation and hence the Zin of the mixer. If you use a voltage source at the RF input the LO-RF leakage will be zero, so can this be an accurate measure of input impedance?

Quote:

Instead I created my own impedance probe by using vsources, isources and ideal-transformer.
This impedance probe is valid not only for Cadence Spectre but also for Agilent RFDE(ADSsim).
And this impedance probe is valid not only for conventional Small Signal AC Analysis but also for Small Signal AC Analysis subjected to Master Large Signal Analysis such as HB-SS of Agilent RFDE(ADSsim) and PSS/PAC of Cadence Spectre.

Would you mind sharing some details on how you set up this probe?

thanks,
Aaron

Title: Re: time variant impedance in a passive mixer
Post by pancho_hideboo on Apr 24^th, 2009, 10:46pm

aaron_do wrote on Apr 24^th, 2009, 10:21pm:

I was thinking that we can leave the output open circuit (or whatever the desired load is), and use a port at the RF input.
Is this setup ok for measuring Z11?

No, you are misunderstanding.

Resistance of "analogLib/port" surely acts as load in PSS of Cadence Spectre.
When you evaluate Z-parameters using PSP, you can't ignore this unpreferable load effects.
http://www.designers-guide.org/Forum/YaBB.pl?num=1231854969/5#5

This is because PSP is slave analysis of master analysis PSS.
You yourself also mentioned this effects in PSS in your another comments.

If you create switch using Verilog-A which operations are OFF for PSS and ON for PSP, you can use PSP without loading at nodes.

Quote:

// This module is valid only for Cadence Spectre
`include "discipline.h"
`include "constants.h"
module ac_switch(vp, vn);
inout vp, vn;
electrical vp, vn;

analog begin
if( analysis("ac", "pac", "qpac",
"xf", "pxf", "qpxf",
"sp", "psp", "qpsp",
"noise", "pnoise", "qpnoise") )
V(vp, vn) <+ 0.0;
else
I(vp, vn) <+ 0.0 ; // V(vp, vn) <+ 1.0T * I(vp, vn);
end // analog

endmodule

On the other hand, you can use ports directly to evaluate Z and Y parameters in conventional SP-Analysis as far as ports don't affect DC bias.

aaron_do wrote on Apr 24^th, 2009, 10:21pm:

Also, I was thinking that the LO leakage to either RF or IF ports can affect the operation and hence the Zin of the mixer.

Right.
http://www.designers-guide.org/Forum/YaBB.pl?num=1193135745/3#3

aaron_do wrote on Apr 24^th, 2009, 10:21pm:

If you use a voltage source at the RF input the LO-RF leakage will be zero, so can this be an accurate measure of input impedance?

Impedance Probes don't shorten any terminals. See Fig. A.2 at page.32 of http://www.rdmiddlebrook.com/downloads/GFTManual.pdf
Impedance Probes are inserted like following.

[Source_Impedance or Previous_Stages]=[Diff_Imp_Probe]=[Mixer]=[Diff_Imp_Probe]=[Next_Stages]
||
[Diff_Imp_Probe]
||
[VCO]

Here [Diff_Imp_Probe] don't shorten [Source_Impedance or Previous _Stages].
In this way, I can evaluate Zleft_diff, Zleft_comm, Zright_diff and Zright_comm at same time without any affect to original electrical connections of circuits.

Title: Re: time variant impedence in a passive mixer
Post by aaron_do on Apr 27^th, 2009, 1:22am

I understand what you mean now. Thanks for sharing.

Aaron

Title: Re: time variant impedence in a passive mixer
Post by pancho_hideboo on Apr 30^th, 2009, 10:47pm

This is an Interstage Differential Impedance Probe.

Title: Re: time variant impedence in a passive mixer
Post by aaron_do on May 4^th, 2009, 8:51pm

Hi pancho_hideboo,

I'm having a little trouble implementing the impedance probe. I figured I could create the probe using the opposite of the ac_switch which you showed me. So the modified code is,

Quote:

`include "constants.vams"
`include "disciplines.vams"

module ac_switch(vp,vn);
inout vp;
electrical vp;
inout vn;
electrical vn;

analog begin
if( analysis("ac", "pac", "qpac",
"xf", "pxf", "qpxf",
"sp", "psp", "qpsp",
"noise", "pnoise", "qpnoise") )
I(vp, vn) <+ 0.0;
else
V(vp, vn) <+ 0.0 ; // V(vp, vn) <+ 1.0T * I(vp, vn);
end // analog

endmodule

The arrangement for the impedance probe is shown in the attachement. The two isin components have an AC and PAC magnitude of 1 A. So I should be able to simply probe the differentical voltages RIGHT and LEFT in order to see the impedance.

I tried to test the probe in a simple AC circuit and there were errors with the AC simulation. If I run the DC analysis alone there is no problem. However, when running the AC analysis, there were errors in finding the DC solution for the AC analysis. The errors are shown below. (this was after a number of lines saying zero diagonal found in Jacobian at 'net020' and 'net 020', Reordering Jacobian, Extrapolation Failed).

Quote:

Error found by spectre during DC analysis, during AC analysis `ac'.
Matrix is singular (detected at `net017').
No DC solution found (no convergence).

The values for those nodes that did not converge on the last Newton iteration are given below. Also given is the manner in which the convergence criteria were not satisfied in the following form:
Failed test: | Value | > RelTol*Ref + AbsTol

V(VDD) = 0 V
residue too large: | -1.50432 A | > 7.52162 mA + 1 pA
I(I98.L0.Lsub3:1) = 0 A
residue too large: | 650 mV | > 3.25 mV + 1 uV
V(I98.L2.6) = 0 V
residue too large: | 54.4945 mA | > 272.472 uA + 1 pA
V(I98.L2.62) = 0 V
residue too large: | 203.77 mA | > 1.01885 mA + 1 pA
V(I98.NM0.D0.dsxnb:int_a) = 0 V
residue too large: | 1.01 A | > 5.05 mA + 1 pA
I(I98.NM0.M0.LBULK:1) = 0 A
residue too large: | -500 mV | > 2.5 mV + 1 uV
V(I98.R1.11) = 0 V
residue too large: | 236.06 mA | > 1.1803 mA + 1 pA
I(I117.M0.LDRAIN:1) = 0 A
residue too large: | -650 mV | > 3.25 mV + 1 uV
I(I118.M0.LDRAIN:1) = 0 A
residue too large: | -650 mV | > 3.25 mV + 1 uV

So anyway I figure that one way to fix this is to get the AC analysis to read the DC solution from the DC analysis. Is there any way to do this? Also, is there a better way to solve this problem?

thanks,
Aaron

Title: Re: time variant impedence in a passive mixer
Post by pancho_hideboo on May 7^th, 2009, 8:49am

aaron_do wrote on May 4^th, 2009, 8:51pm:

I'm having a little trouble implementing the impedance probe.
I figured I could create the probe using the opposite of the ac_switch which you showed me.
[snipped]
The arrangement for the impedance probe is shown in the attachement.
The two isin components have an AC and PAC magnitude of 1 A.
So I should be able to simply probe the differentical voltages RIGHT and LEFT in order to see the impedance.

You still don't understand interstage impedance probe.

In your schematic, your switch cut signal path.
Interstage impedance probe never cut any signal path.
Interstage impedance probe is basically same as measurement method of loop gain where any signal path is never cut.
Again see Fig. A.2 at page.32 of http://www.rdmiddlebrook.com/downloads/GFTManual.pdf

As I wrote in the following, my impedance probe is composed of combination of vsources, isources and ideal-transformer.
http://www.designers-guide.org/Forum/YaBB.pl?num=1240334878/10#10

I don't use any analysis specific switch in my Interstage impedance probe.

The reason why I showed analysis specific switch by Verilog-A in the following is to avoid unpreferable load effects in PSP and QPSP.
http://www.designers-guide.org/Forum/YaBB.pl?num=1240334878/16#16

Title: Re: time variant impedence in a passive mixer
Post by lorenzo on Aug 25^th, 2010, 2:36am

pancho_hideboo wrote on Apr 30^th, 2009, 10:47pm:

This is an Interstage Differential Impedance Probe.

I have been reading those interesting post and currently I am interested into looking inside the box to see how you implemented the differential impedance probe. I look at the Middlebrook, but I am not sure the way you derive your proble, can you share it with us in more details ? Thanks

Title: Re: time variant impedence in a passive mixer
Post by aaron_do on Aug 27^th, 2010, 1:19am

Hi,

pancho_hideboo said that he used an ideal transformer. I tried doing a impedance probe using the component xfmr from analogLib in cadence, but it seems that the xfmr component also passes DC. So I ended up using an ideal inductor to sense the AC current. I think that an ideal xfmr is in a way acting as a simulation dependent component, so perhaps the AC switch is another way to do it. I never ended up getting my AC switch to work though.

This is what I finally understood from pancho_hideboo's hints, but i'm not sure if its really correct. See attachment. I forgot to write the port names, but you get the idea. Also, I guess the simulator finds it easier if you use an ideal transformer since there's no frequency dependence (i think).

cheers,
Aaron

Title: Re: time variant impedence in a passive mixer
Post by lorenzo on Aug 27^th, 2010, 2:58am

Thanks,
I'll give it a try, how are you supposed to derive the impedance?
I guess you just measure voltage across the left pins for Zleft and right pins for Zright?
btw, I downloaded the Middlebrook paper...jeee it will take me a while to read it all :) but I guess it's worth.
Cheers

Title: Re: time variant impedence in a passive mixer
Post by aaron_do on Aug 27^th, 2010, 5:29pm

Hi,

yeah just measure the voltage. Anyway hopefully I didn't misunderstand anything from what pancho_hideboo said, but that's the schematic I interpreted. Seems to work...

cheers,
Aaron

Title: Re: time variant impedence in a passive mixer
Post by pancho_hideboo on Aug 28^th, 2010, 8:34am

lorenzo wrote on Aug 25^th, 2010, 2:36am:

I look at the Middlebrook, but I am not sure the way you derive your proble,
can you share it with us in more details ?

Attached figure with mosaic is a Hint-1.

The following is a Hint-2.
http://www.designers-guide.org/Forum/YaBB.pl?num=1231344965/1#1

The following is a Hint-3.
But in my Impedance Probe both current and voltage excitations are implemented at same time.
http://www.designers-guide.org/Forum/Attachments/summarytb.pdf

If only current excitation is invoked, we can't measure very small impedance(e.g. short) correctly.
Vice versa, if only voltage excitation is invoked, we can't measure very high impedance(e.g. open) correctly.

The followings are general notes for you.

- Always describe correct tool's name and vendor's name which you use as tool or simulator.
- 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

Title: Re: time variant impedence in a passive mixer
Post by aaron_do on Aug 30^th, 2010, 2:10am

Hi pancho_hideboo,

one thing i'm confused about (among other things). Won't your probe disturb the DC conditions of the circuit? Or are your current/voltage probes only measuring the AC signal? If so could you say how this is done?

Also, you mentioned you are implementing the voltage and current exitations at the same time. I noticed you have 8 outputs, but I can only see the need for four (common/differential mode Zleft and Zright). Are you providing two options for each one? i.e. one with current exitation and one with voltage exitation?

thanks,
Aaron

Title: Re: time variant impedence in a passive mixer
Post by pancho_hideboo on Aug 30^th, 2010, 5:04am

aaron_do wrote on Aug 30^th, 2010, 2:10am:

Won't your probe disturb the DC conditions of the circuit?

Not at all.

aaron_do wrote on Aug 30^th, 2010, 2:10am:

Or are your current/voltage probes only measuring the AC signal?

Yes.

aaron_do wrote on Aug 30^th, 2010, 2:10am:

If so could you say how this is done?

By using small signal sources for conventional small signal analysis
and slave small signal analysis for master large signal periodical steady state analysis.

aaron_do wrote on Aug 30^th, 2010, 2:10am:

I noticed you have 8 outputs,
but I can only see the need for four (common/differential mode Zleft and Zright).

Not correct.
Eight quantities are needed for evaluation of Zleft_com, Zleft_diff, Zright_com and Zright_diff.

Zleft_com=Vleft_com/Ileft_com
Zleft_diff=Vleft_diff/Ileft_diff

Zright_com=Vright_com/Iright_com
Zright_diff=Vright_diff/Iright_diff

Title: Re: time variant impedence in a passive mixer
Post by aaron_do on Sep 7^th, 2010, 12:45am

Hi pancho_hideboo,

it seems that your circuit may be less complicated than I originally thought. You earlier pointed to a reference to Middlebrook's general feedback theorem, and it led me to believe that your circuit is doing some kind of null-double-injection. However, after going over your circuit (the mosaic), it seems that you are simply doing the following:

1) split the signal into common-mode and differential-mode branch.

2) For each branch, inject a small signal current and voltage (both appear to be derived from a single small-signal source.

3) Zleft_common = Vleft_common/Ileft_common (the other impedances are similarly calcualted).

Am I still misunderstanding your probe?

Also, you mentioned earlier that only injecting a current would result in inaccuracy when measuring small impedances (and vice versa). Is this some kind of rounding error in the simulator's calculations?

thanks,
Aaron

Title: Re: time variant impedence in a passive mixer
Post by pancho_hideboo on Sep 7^th, 2010, 2:12am

aaron_do wrote on Sep 7^th, 2010, 12:45am:

1) split the signal into common-mode and differential-mode branch.

Correct.

aaron_do wrote on Sep 7^th, 2010, 12:45am:

2) For each branch, inject a small signal current and voltage
(both appear to be derived from a single small-signal source.

Correct.

aaron_do wrote on Sep 7^th, 2010, 12:45am:

3) Zleft_common = Vleft_common/Ileft_common
(the other impedances are similarly calcualted).

Correct.

aaron_do wrote on Sep 7^th, 2010, 12:45am:

Also, you mentioned earlier that only injecting a current would result in inaccuracy when measuring small impedances (and vice versa).

Simply consider a case where Zleft=0 and Zright!=0.
All injected current flow into Zleft.
So we can't measure Zright.

Title: Re: time variant impedence in a passive mixer
Post by aaron_do on Sep 7^th, 2010, 4:58am

thanks for the help

Aaron