sharpak
Newbie level 3
Hi guys
It is known than telescopic or folded cascoded amplifiers bring a very high DC gain (gm²/gds²) when a "simple" differential pair gives a "gm/gds" dc gain.
In open loop, it is better to casAcde 2 stages than using a single cascode if we want to prevent from speed limitations. That is quite clear and OK.
In closed loop, we do have a choice. Let's suppose we are not swing limited (vdd = 3P3 volts for example). And let's suppose our system is reset every 10µs to be active for 10µs.
I may be wrong, but Fourier transformation say that we got a sort of door function. The frequency equivalent would be a sinus cardianal whom main energy would be large of 100 kHz (between 1/T and -1/T) .
DOes it mean that the system will see any signal from 0 to 100 khz and that so, the low frequency will affect the amplifier response quality?
Or should we understand the following: the system work at a frequency of 100 kHZ. So, there is no way the DC gain may influe on the closed loop response. Indeed, closing the loop, the pole are moving to cut at gm/CLoad for Both amplifiers. And we are then far above the cut frequancy of both amplifers, in a frequency area where folded cascoded and differential pair transfer function are exactly the same.
I'm very confused cause i tried some transient simulations, but i wouldn't see any effect between cascoded and fiderential, if not a better linearity for ..the differential pair.
---------- Post added at 16:38 ---------- Previous post was at 15:30 ----------
huuuh...nobody got any idea? Just even a clue?...
It is known than telescopic or folded cascoded amplifiers bring a very high DC gain (gm²/gds²) when a "simple" differential pair gives a "gm/gds" dc gain.
In open loop, it is better to casAcde 2 stages than using a single cascode if we want to prevent from speed limitations. That is quite clear and OK.
In closed loop, we do have a choice. Let's suppose we are not swing limited (vdd = 3P3 volts for example). And let's suppose our system is reset every 10µs to be active for 10µs.
I may be wrong, but Fourier transformation say that we got a sort of door function. The frequency equivalent would be a sinus cardianal whom main energy would be large of 100 kHz (between 1/T and -1/T) .
DOes it mean that the system will see any signal from 0 to 100 khz and that so, the low frequency will affect the amplifier response quality?
Or should we understand the following: the system work at a frequency of 100 kHZ. So, there is no way the DC gain may influe on the closed loop response. Indeed, closing the loop, the pole are moving to cut at gm/CLoad for Both amplifiers. And we are then far above the cut frequancy of both amplifers, in a frequency area where folded cascoded and differential pair transfer function are exactly the same.
I'm very confused cause i tried some transient simulations, but i wouldn't see any effect between cascoded and fiderential, if not a better linearity for ..the differential pair.
---------- Post added at 16:38 ---------- Previous post was at 15:30 ----------
huuuh...nobody got any idea? Just even a clue?...
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