What type of opamp is more suitable for achieving high PSSR?

[surianova]

PSSR

hi all,

I have one question regarding the design of voltage regulator.
To design a regulator we need a opamp to regulate the volatge.
What type of opamp is the more suitable to acheive high PSSR
(power supply rejection ratio)? Two stage amplifier? cascode
two amplifier, or folded cascode amplifier? Thanks in advance.

Suria

 

[hrkhari]

Re: PSSR

Hi :

PSSR is a common mode noise, hence a differential stage amplifier would be much suitable.

Rgds

 

[surianova]

Re: PSSR

Yes, we must use the diffrential opamp,but the question is which opamp have the best PSSR? TX

Suria

 

[hrkhari]

Re: PSSR

It depends on the application of the designed circuitry. If you are more particular ob the issues of input-output isolation and high output impedance use a differential cascode stage. Pls specify the application type

Rgds

 

[surianova]

Re: PSSR

The aplication of the opamp is for negative feedback of the regulator to provide constant output. And i do no want the noise of the power suppy to effect the regulator output. Is this folded opamp is better? or cascode opamp?

 

[cetc1525]

PSSR

someone said using a wide band &high gain op.

 

[hrkhari]

Re: PSSR

Due the application of dc feedback, I think a typical differential stage OpAmp would serve the purpose. If the frequency of application is high, a cascode stage differential OpAmp would serve the purpose

Rgds

 

[surianova]

Re: PSSR

If the frequency of application is high, a cascode stage differential OpAmp would serve the purpose

By using cascode will provide high gain but reducing the bandwitdh.

 

[jiangwp]

PSSR

The cascode stage op and the fold-cascode are the selection for high PSRR. but there are some factors to trade off . They are power dissipation, speed , bandwidth or slew rate.

 

[Junus2012]

Any Op-Amp that not introduce a compensation capacitor will has better PSRR, the reason behind that is the C.C....
therefore a single pole OTA Like folded will be good choice but in the cost of power.

 

[gasingh]

Re: PSSR

Hi :

PSSR is a common mode noise, hence a differential stage amplifier would be much suitable.

Rgds

hrkhari , Power Supply Noise is not really a 'Common-Mode Noise ' , in the sense it is not a noise common to both the inputs of a differential Amplifier , To analyze the PSRR of an opamp you need to consider two cases , Noise on VDD and Noise on VSS , in each case the small signal model will decide what portion of noise is coupled to the output . You can read the section 6.4 and 6.5 of the Allen Holberg book and then appreciate better how cascoding helps in reducing PSRR

Rgds

 

[Junus2012]

Re: PSSR

hrkhari , Power Supply Noise is not really a 'Common-Mode Noise ' , in the sense it is not a noise common to both the inputs of a differential Amplifier , To analyze the PSRR of an opamp you need to consider two cases , Noise on VDD and Noise on VSS , in each case the small signal model will decide what portion of noise is coupled to the output . You can read the section 6.4 and 6.5 of the Allen Holberg book and then appreciate better how cascoding helps in reducing PSRR

Rgds

Yes you are right, the common mode noise is that noise common to the two inputs of the opamp, while the PSRR is referred to the noise that affecting the output from the power supply terminals and hence we have +PSRR and -PSRR

 

[varunkant2k]

Re: PSSR

hi all,

I have one question regarding the design of voltage regulator.
To design a regulator we need a opamp to regulate the volatge.
What type of opamp is the more suitable to acheive high PSSR
(power supply rejection ratio)? Two stage amplifier? cascode
two amplifier, or folded cascode amplifier? Thanks in advance.

Suria

Hi Suria, Most of your query already cleared by above posts. To give more clear answer to your question, Folded cascode amplifier with high open loop gain should be best choice.
PSRR is directly related with the gain of OPAMP.
Off course Differential stage helps in rejecting supply common mode noise.
Generate differential stage biasing to Folded casode stage, that will help you to achieve better PSRR.