50 ohm buffer 10MHz to 40 MHz (wafer probe)

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Hi,
I want to design a 50 ohm buffer in frequency range 10MHz-40MHz which will be followed by wafer probes and then instruments. The baseband output of a receiver will be buffered.

I am planning for PMOS source follower with
a) current source load
b) resistive load

PMOS for low flicker noise. Which one is better a) or b).
Any other suggestion? I have no power limit. I need low noise.
 

Last edited:

If your requirement needs Low Noise, I suggest you to use Bipolar transistor at those frequencies if available.
Otherwise CMOS may be trouble..
 

Hi SunnySkyguy & BigBoss,

Thank you very much for your suggestions! I am using PMOS due to time constraints.
I have attached the circuit. i am using 3.3V I/O PMOS devices in 65nm process. The bias current is 5mA.

1. Is the current too high?

2. gm of M1 =1/Rload=1/50 (for S11=-15dB)

Gain=gm*Rload/(1+gm*Rload)=0.5
Is there a way to increase gain without matching circuit?

3. The sizes are
(w/l)1=600u/400n
(w/l)2,3,4,5=400u/400n
Is it ok to have different length devices in current source & M1? I am worried since thresholds may not track each other.

Is the design OK?

 

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