[SOLVED] Balun-LNA Single to Differential LNA Cadence setup

[Avinash Akotkar]

I am working on "inductor less" Balun LNA Single input - Differential ended amplifier on 130nm for 433MHz. Attached IEEE transaction paper for same

Balun-LNA Schematic:

Here is my question:
1. In testbench, i used VCVS to convert differential to single ended so that I can do S-Parameter analysis on Two ports

Output I got: NF:3dB, S21=16dB, S11=-10dB but S22 is -3dB which is strange, I tried tuning load resistor as results other parameters impacted but S22 remains intact

2. Now Instead of VCVS I used balun for rflib, here other parameters like S22. S11, NF comes fine but S21 comes in -3dB (very strange)

So with both VCVS and balun I am getting different results,

Can anyone please help correct setup for Balun-LNA (Single-Differential) Testbench setup, I am stuck with this problem, if any user guide for same also helpful

 

[volker@muehlhaus]

1. In testbench, i used VCVS to convert differential to single ended so that I can do S-Parameter analysis on Two ports

What is the input impedance into this load, i.e. into the controlled source?

 

[Avinash Akotkar]

What is the input impedance into this load, i.e. into the controlled source?

Thanks for response, I done ac analysis with 1mV as input

signal OP("/E0" "??")
i -12.7676m
lx0 638.38m
lx1 -12.7676m
lx2 638.38m
pwr -8.15058m
v 638.38m

If v/i = 638.38m/12.76 = ~53 ohm

Again, I am not sure it this setup is correct or not Balun-LNA because VCVS or Balun gives different results

 

[volker@muehlhaus]

I meant the input impedance seen by your Diff_Amp subcircuit into the controlled source. My guess is that your amp sees infinite impedance into the VCVS control input, whereas the balun input represents the proper load.

If I am right, results should agree if you add proper differential load resistance at VCVS input.

 

[Avinash Akotkar]

Thanks for response, I assume balun setup is correct one for testbench .....right
Any suggestion , I mean how to improve S21 by looking into schematic (All other parameters are good as per specification but not S21)
and I want to improve it without inductor

 

[dick_freebird]

I think shunt terminating the vcvs input and source
terminating the differential vcvs output (the compound
voltage source E0 shows an R, is that value populated
right?) might be the ticket.

The vcvs control terminals are infinite impedance so
your amp block output will be making up its own
ideas about common mode, and if you think those
series resistors (R0 / R1) will be completing a current
loop through them and those pins, fuggedaboudit.
Output is effectively an open for current, and if the
amp needs to throw current through or to somewhere,
to work, ain't gonna happen.

 

[BigBoss]

That Balun passes DC.So OP is not maintained in your circuit.
You don't have to use neither Balun nor VCVS. You can connect Port element to the circuit with an appropriate large capacitor. Port element is differential in Cadence ADE, not grounded.

 

[Avinash Akotkar]

That Balun passes DC.So OP is not maintained in your circuit.
You don't have to use neither Balun nor VCVS. You can connect Port element to the circuit with an appropriate large capacitor. Port element is differential in Cadence ADE, not grounded.

Thanks for inputs. I tried with below setup with cap value 8pF. Request to please check if its right one or not... getting worse value of S21= -7dB
If its correct setup then I will update core schematic

One more thing, I was just playing around vcvs, added 10ohm resistance at its output then surprisingly I was getting good results

Request to guide me over here

 

[BigBoss]

Thanks for inputs. I tried with below setup with cap value 8pF. Request to please check if its right one or not... getting worse value of S21= -7dB
If its correct setup then I will update core schematic


One more thing, I was just playing around vcvs, added 10ohm resistance at its output then surprisingly I was getting good results



Request to guide me over here

Mr. Akothar,
You should connect 2 serial capacitors to block DC on both ways. This capacitor value may have 1nF or more just to block DC current.
Stop to use VCVS or Balun. Cadence ADE Port element is already differential, no need to use a Balun or something else.
Connect the Port element with serial 2 capacitors, that's it.

 

[volker@muehlhaus]

.... and if you use the port fot the differential signal, don't forget to set the differential impedance in the port.

 

[Avinash Akotkar]

Mr. Akothar,
You should connect 2 serial capacitors to block DC on both ways. This capacitor value may have 1nF or more just to block DC current.
Stop to use VCVS or Balun. Cadence ADE Port element is already differential, no need to use a Balun or something else.
Connect the Port element with serial 2 capacitors, that's it.

Thanks for update. I will follow these instruction. I am not getting desired output, I have given parametric analysis simulation for few components.
I will update once simulation over for same.

--- Updated Mar 7, 2025 ---

.... and if you use the port fot the differential signal, don't forget to set the differential impedance in the port.

Thanks but I am using IC231 cadence virtuoso, I don't see any option to set "differential". I think by default its differential as mentioned by BigBoss

 

[volker@muehlhaus]

Thanks but I am using IC231 cadence virtuoso, I don't see any option to set "differential". I think by default its differential as mentioned by BigBoss

You don't understand well. I'm talking about impedance. The differential output has 2 * 50 Ohm = 100 Ohm impedance, so you need to set 100 Ohm in the port.

 

[Avinash Akotkar]

You don't understand well. I'm talking about impedance. The differential output has 2 * 50 Ohm = 100 Ohm impedance, so you need to set 100 Ohm in the port.

Ohhh... that's my fault... this is where I need all of your assistance. I have updated output port with 100 ohm (differential port) and input port with 50 ohm (single input single)

 

[Avinash Akotkar]

Hello Team,

With mentioned testbench and differential port, and after doing parametric analysis, I am getting good NF 2.78dB, but not much good S21=4.54dB, I am expecting >10dB
Is any way to improve this, I tried by tuning width of mosfet and other passive components but its not going beyond this