about design and test of low noise low distortion amplifiers

[wonbef]

hi,all:

pls recommend some materials/methods about the design of low noise and low distortion amplifiers, and how to test the noise of amplifier itself. thanks.

regards
04/14/2005

 

[Vamsi Mocherla]

Re: about design and test of low noise low distortion amplif

Dear wonbef,

Low Noise and Low distortion are two different concepts. Distortion is mostly controlled by how your output drivers are driving. Low noise requires more bulkier input differential pair. But there is one common thing, between the two conditions. We need to have ample current in each branch in the circuit. That reduces the thermal noise component and also takes care of delivering enough current to the load.

So, the best suggestion would be to design an amplifier with :

1. Huge W/Ls for the input pair
2. Large current drivers at the output stages.
3. More current in the current devices. Hence their sizing is also larger.

I hope that I am clear and it helps........

 

[wonbef]

Re: about design and test of low noise low distortion amplif

Hi,Vamsi Mocherla:
many thanks in advance! because of single-end input in my system, so a single-to-differential opamp needed, i think the distortion resulted from this circuit. do you have good ideal for this single-to-differential opamp with low distortion?

regards,
wonbef

 

[Vamsi Mocherla]

Re: about design and test of low noise low distortion amplif

What a lot of people do when they need a single ended to differential swing is that, they use another opamp with gain =-1 in addition to your main amp. This would generate an equal and opposite swing.