telescopic with folded cascoded gain boosted

[houda09]

gain boosted problem

hello i want to design telescopic with folded cascoded gain boosted , I make these simulations results listed in the file joined, but the gain doesn't increased. What's the problem.

 

[alfredop]

gain boosted problem

You are not providing any useful information about your design for anyone to be able to help you.

 

[houda09]

Re: gain boosted problem

hello,
i want to design an OTA with high gain and high bandwidth to use it after in high speed delta sigma modulator. I want to design telescopic gain boosted with folded cascode OTA. The TGBO will reached 100dB dc gain and about 700MHz GBW. I design with 0.35um 2.8V technology. I designed the main amplifier which is the telescopic OTA, it presents a dc gain of 53.7dB, a GBW of 710 MHZ, a dominent pole of 1.8Mhz, a margin phase of 70 deg, a biais current of 1100uA, a Vdd of 1.4V (Vdd=-Vss=1.4V) and a load capacitance of 1.5pF. I designed the first gain boosting folded cascode OTA with nmos input, it presents a dc gain of 60.57dB, a GBW of 561 MHZ, a dominent pole of 0.58Mhz, a margin phase of 63.5 deg, a biais current of 1008uA, a Vdd of 1.4V (Vdd=-Vss=1.4V) and a load capacitance of 2.5pF. After that, i designed the seconf gain boosting folded cascode OTA with pmos input, it presents a dc gain of 60dB, a GBW of 566 MHZ, a dominent pole of 0.63Mhz, a margin phase of 63.5 deg, a biais current of 1108uA, a Vdd of 1.4V (Vdd=-Vss=1.4V) and a load capacitance of 2pF. When i collect the folded cascode OTA gain boosting with the telescopic and i simulate the overall amplifier, the gain doesn't increased, i don't find the problem. I simulate with ORCAD PSPICE (bsim3v3 model).
Could you please help me.
best regards
houda

 

[strennor]

gain boosted problem

could you show your circuits?

no improvement after the gain boost amps are inserted? does it mean the two amps don't work at all? could you check your DC operation point?

 

[houda09]

Re: gain boosted problem

hello,
thank you for your reply, the gain of the overall ota is not increased,
this a joined file.
best regards

 

[rage_speed]

gain boosted problem

Hi houda09,

The problem I think is that M3,M4,M5,M6 of the main telescopic opamp are diode connected.

Inorder to get the gain boosting the gates of these should be connected to the output of the gain boosting amplifiers.

 

[houda09]

Re: gain boosted problem

Dear sir,
i connect the gates of these transistors to the output of transistors but no results. The problem the overall amplifier run normally when the frequency of the telescopic ota is about 350MHz, but i need to simulate it with above 500MHz. I don't find the problem.
best regards

 

[rage_speed]

gain boosted problem

I am not sure if the 2pf & 1.5pf capacitors should be present at the outputs of the gain boosting amplifiers.

And also since the gain bandwidth product is constant you need to decrease the gain(Rout) to increase the bandwidth.

 

[solidstate]

gain boosted problem

Like strennor said, what about your DC operating point? It seems you have no common-mode feedback for your main OTA nor for the booster amplifiers, so I suspect not all your devices are operating in saturation.. can you post the dc voltages with the circuit?