If the input to the buffer is a 3 GHz signal with common mode 1.2v, the output of buffer will connect to RC low pass filter to extract DC value 1.2v, which configuration you sugest to use?
Thanks in advance.
Suria
1) the reason i use buffer:-
The main signal 3 GHz will fed to other block for processing but i need
to extract the DC value for control purpose in other block. So, i just
put a buffer between the 3 GHz signal and LPF filter so that the 3
GHz signal will not be loaded by the LPF. The LPF i have is the resistor
connect in series with capacitor. The cufoff frequency for LPF is 30 KHz.
And i am not sure, we need buffer or not in this case?
2) If we want to connect 2 block together, what is the consideration
for input and output impendence ?
JPR said:I would recommend that you keep 1/(2*pi*R*C) > 30GHz to keep from impacting phase at 3GHz, with R being your series resistor and C being the input capacitance of the amplifier. This is especially true if input signal is greater than 100Ohms impedance at 3GHz.
JPR said:If your circuit can handle it, put a resistance to the input of the amplifier, to keep capacitance from impacting signal to the other block
JPR said:The need for a buffer depends upon the levels of impedance and your requirements for accuracy. If you have a 0.1% requirement for accuracy, the input impedance (again, across your frequency of interest) must be greater than 1000x the output impedance of the previous stage. If your requirement is tighter, you will need a larger ratio, and if your requirement is more relaxed, you can have a lower ratio. Since input impedances are usually MUCH higher than output impedances, this is typically not much of an issue.
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