NF (SSB or DSB) in receiver chain.

[wccheng]

nf dsb

Dear all,

As I asked before, I have designed a receiver chain included, Tx/Rx switch + LNA + Mix1 (low IF) + Mix2 (zero IF). In the overall receiver simulation, I should see the NF value in SSB or DSB? It is because mix1 is low IF and mix2 is zero IF.

Thanks

 

[wccheng]

nf ssb dsb

In my simulation setting, I have set LO1=2.112GHz, LO2=1.32GHz. The RF frequency range is 3.168GHz - 3.696GHz. I am using spectrerf simulator. I have set RFinputC, LO1=2.112GHz and LO2=1.32GHz. Then it uses QPSS + QPNoise. In the QPNoise, I set the output frequency sweep range is 1M to 264M. Am I correct?

 

[vfone]

ssb dsb nf

Because the first conversion is Low-IF the final noise is DSB (including the image noise)

 

[UWB_man]

dsb nf

I think you can't use only SSB NF or DSB NF measurement in the overall receiver simulation, because the first mixer has SSB NF and the second mixer has DSB NF. You should try to use NF definition (NF = 10lg(SNR_in/SNR_out)), but i don't know how to do it exactly in you software.

 

[wccheng]

nf ssb

Because my design specification, the NF is around 4.8dB. If the simulated NF is using SSB value, I could not get the required value even I tune my circuit. If I use DSB value, it could reach the result. So, I am so confusion that what NF simulated value I should use in this two mixers zero-IF receiver. Could any expert give me hint?

thanks

 

[UWB_man]

dsb nf

also you can divide the receiver chain by 2 parts:
1 - rx/tx switch, lna, mixer1 (use SSB NF)
2 - mixer2 ...(use DSB NF)
and calculate NF for each part separately (no dB, in times). total NF_tot=NF1+(NF2-1)/G1, where G1 - power gain of first stage. use 10lg(NF_tot) for convert to dB.

 

[wccheng]

tx dsb

Dear UWB_man,

I agree with your reply. However, I have some questions about the NF and power gain simulation if they simulated separately. If I simulated the power gain of first stage, I need to give a 50ohms port to get a S21. However, the output of the first stage is connected to the input of stage2 originally. How could I simulate it correctly?

thanks

wccheng

 

[UWB_man]

nf1+(nf2-1)/g1

I think you should measure the power gain and the NF of the first stage with 50Ohm ports. Then you should measure output impedance of the first stage (it's output impedance of mixer1) Zout1. The NF of the second stage should be measured with the input port impedance Zin2 = Zout1! I checked this method and got good results. I hope this is useful for you.

PS The S21 isn't the power gain, i think you should use special power gain measurement (Gp = Pdelivered_to_the_load/Pinput_to_the_network).

 

[wccheng]

receiver ssb

Hi UWB_Man,
For the Cadence platform, the port just allow us to enter the resistance value. I could not input the imaginary part. How could I make Zin2 = Zout1? It is because the Zout1 maybe Real+j*Imaginary. I am using icfb5141 + mmsim61.
Thanks