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Circuit biasing problem

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promach

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How to bias this circuit correctly ?

Gm2.png
 

promach said:
How to bias this circuit correctly ?
Click to expand...

Where? M5 has its bias voltage already. What's your Vdd ? Do you want it operate in open or closed loop? Which gain is required?
 

Vdd = 3.3V and closed loop operation. Large-signal gain or small-signal gain ? I guess I need to read some books to get the relevant gain equations.

Additional Information:

This diferential circuit is connected in negative feedback manner to a CMOS inverter.
 


frequency_trap.png

This is the overall schematics.
 

What do you intend with this circuit? If the X1 circuit actually is a digital inverter cell, it won't operate in linear mode. It could perhaps transform your sinusoidal input into a square wave output.
 

As far as I know, X1 is not a pure digital inverter cell.

CMOS_inverter_X1.png

- - - Updated - - -

As mentioned in https://www.edaboard.com/showthread.php?t=348802&p=1489127&viewfull=1#post1489127, could you elaborate on it ? inductor for open-loop gain measurement ? and how is CMFB circuit used in this case ?

Besides, it seems like I have a similar differential amplifier as in Figure 4.54(a) below:

Why does the first term of A1 ends up as Ad while the second term ends up as Acm ?

Screenshot from 2017-10-12 17-59-53.png
 

promach said:
As far as I know, X1 is not a pure digital inverter cell. View attachment 141769
Click to expand...
As long as there's no feedback around it, it's considered pure digital.

promach said:
As mentioned in https://www.edaboard.com/showthread.php?t=348802&p=1489127&viewfull=1#post1489127, could you elaborate on it ? inductor for open-loop gain measurement ?
Click to expand...
I think it's well explained; a standard method for open-loop gain measurement. Reread it thoroughly, and read about it in any Analog Circuit Design textbook.
If you need more explanation, you should exactly tell about what.

promach said:
and how is CMFB circuit used in this case ?
Click to expand...
By control of the head or tail transistors.

promach said:
Besides, it seems like I have a similar differential amplifier as in Figure 4.54(a) below:
Why does the first term of A1 ends up as Ad while the second term ends up as Acm ?
Click to expand...
These are the definitions of the differential and common mode gain (or rather: transimpedance).
 

ok, let me read more on application of CFMB circuitry.

Is the following test circuit the right way to measure open-loop gain of my Gm2 circuit block ? note: now I have asymmetrical input rather than symmtrical differential pair

Screenshot from 2017-10-12 20-04-41.png
 

Yes, it's fine - if your amplifier is able to sustain an output common mode voltage OCMV=V2. A correctly dimensioned amplifier with feedback controlled gain |A|=1 (via L1 in your above circuit) will do it.
 

For a DC feedback gain of -1 , the amp output must be able to achieve an OCMV same as the DC non-inverting input voltage. So simple!
 

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