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Help me increase the input range of a telescopic op-amp

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firsttimedesigning

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so i have designed a telescopic op-amp (please see the attached file),
the problem with the op-amp is that its input range is very limited (-0.7V to -1V).

Any suggestion on increasing the input range? I would like it to be from -0.5V to 0.5V.

Any help is appreciated, thanks.
 

telescopic op amp why called telescopic

What's ur supply voltage?
 
telescopic op amp

Hi
you can increase upper limit by using folded cascode architecture.
regards
 
telescopic op

I agree, the best solution would be to increase the supply range.
Are you allowed to use a new stage solve the problem, because if you can, you may design a circuit.
 
telescopic opa

if you decrese Iss the overdrives of transistors are reduced and you can increase input range.
 
Re: telescopic op-amp

well thank you all for replying...

for savikx,
Vdd = 2V and Vss = -2V

for hr_rezaee,
thank you for the suggestion, currently, i am trying to design a two stage op-amp.
first stage is a differentail amplifier with PMOS current mirror load. second stage is a common source amplifier. based on your experience, can you please tell me that which would have higher input range, two stage op-amp or folded cascode architecture?

for sadegh.j
thank you for the suggestion.
i have increased the supply voltage and the input range is still in that several ,milivolt (mV) range. I would like the input range to be 1V. right now it's about 3mV. I can use any type of architecture that i want. so yes that means i can use an additional stage to solve the problem, which is what i am trying to do now.

for al_valaee
thank you for the suggestion.
i also have tried to decrease the overdrive voltage of transistor M9, which is the current source (Iss). Still, the input range is pretty small. it seems to me that telescopic architure will always have that small input range, which is why i am trying to use another architecture.
 

telescopic op-amp

Hi
I think there is no significant difference.
regards
 

telescopic op-amp

The folded-cascode architecture will be better.
Here is a simple example.
 

telescopic op-amp

Folded cascode is a better option if input voltage swing is the only criteria! And reducing the overdrive voltage for tail is another possibility.. Still the range you are talking is pretty huge to realize when supply voltage is very little! You can realize such large input range when u use the OTA in feed back structure because may be.. Becuase to get larger gain and bandwidth, we need larger gm and we usually increase either current or decrease over drive voltage(pushing input transistor more into sub threshold region).

One more thing.. Did u really biased the PMOS load as u mentioned in the first circuit? It wil severly affect your output swing i suggest.. Better bias it externally as u did for the NMOS load.. Else try better biasing scheme.. I am not fully convinced with the biasing scheme for the PMOS loads! Please do consider it as well..
 

telescopic op-amp

at the same input range you can reach higher gain with folded cascode .
at first you should select your target , gain or bandwith or ... ?

I think folded cascode is better than 2 stage opamp.

for more informations you can check the Martins book about this . it hase both of folded and 2 stage stractures.
 

Re: telescopic op-amp

firsttimedesigning said:
well thank you all for replying...

for savikx,
Vdd = 2V and Vss = -2V

for hr_rezaee,
thank you for the suggestion, currently, i am trying to design a two stage op-amp.
first stage is a differentail amplifier with PMOS current mirror load. second stage is a common source amplifier. based on your experience, can you please tell me that which would have higher input range, two stage op-amp or folded cascode architecture?

for sadegh.j
thank you for the suggestion.
i have increased the supply voltage and the input range is still in that several ,milivolt (mV) range. I would like the input range to be 1V. right now it's about 3mV. I can use any type of architecture that i want. so yes that means i can use an additional stage to solve the problem, which is what i am trying to do now.

for al_valaee
thank you for the suggestion.
i also have tried to decrease the overdrive voltage of transistor M9, which is the current source (Iss). Still, the input range is pretty small. it seems to me that telescopic architure will always have that small input range, which is why i am trying to use another architecture.
Click to expand...

how do you mean your input range is several mV? you said it was 300mV (-1 to -0.7)

what's your output swing, anyway? you obviously have a problem to achieve higher value of common mode voltage Vin_max= Vb-Vgs4+Vt2, and Vb=Vout_min+Vt4, so Vin_max=Vout_min-Vgs4+Vt4+Vt2=Vout_min-Vov4+Vt2.
It may me that you set your Vb to low in order to have maximum output swing.
 

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