Design of low noise op amps at low frequency

[bunda_bindaas]

I need to design a very low noise op amp at low frequencies. Can anyone please help/guide me to relevant papers or journal articles?

Thanks

 

[dsula]

you want to take a look at chopping amplifiers. This will remove your 1/f noise, the dominant noise at low frequency

 

[pfd001]

Large input transistor size will help you to reduce the 1/f noise

 

[jeff_zx]

i think chopping or CDS may be the better choice

 

[safwatonline]

hello,
can u provide a papper or something about chopping

 

[bunda_bindaas]

Thanks for the help but I can not use chopper stabilized techniques for my op amp. But thanks anyway. It seems I can only increase the size and burn more current to reduce the 1/f noise.

 

[beckchm]

you can change first sc circuit to elimate 1/f noise

 

[lily1981216]

hello,
can u provide a papper or something about chopping

i also want to know some about chopping especially in simulation.
how to do noise analysis about chopper amplifier.thanks

 

[wenadinho]

Without chopper stabilization, flicker noise is dominant @ low frequency. We might want to increase the aspect ratio (W/L) and also device area (WxL) of the input transistor. Also, it is necessary to push the mirror transistor in the saturation region and this should be accomplished by increasing the L of the mirror transistor.

With chopper, assuming the corner frequency of the flicker noise is much lower than the chopping frequency, we can safely assume that the flicker noise will be fully removed by the chopper amplifier system. Therefore, in the amplifier design, the objective is to reduce the thermal noise of the system. The reason for this is that the noise spectral density after chopper application can be approximated by noise density of the amplifier at chopper frequency. One way to achieve a lower thermal noise is by increasing the transconductance (i.e. gm) of the input transistor.

Pnoise simulation should be able to simulate a chopper stabilized system.

 

[evi]

I need to design a very low noise op amp at low frequencies. Can anyone please help/guide me to relevant papers or journal articles?

Thanks

A word of caution: to design low noise chopper-stabilized amp, which is going to be switched cap kind of circiuit, you will need fairly high caps to keep the kT/C noise low. This might be difficult to achieve on chip, although it's not a problem if you have an option of using off-chip caps. Another cauiton is that you can't simulate kT/C noise even with pnoise sim, so you will have t calculate the total noise "by hand" as a RMS sum of simulated noise and kT/C noise.

I'm attaching a paper on low noise mic preamp.

 

[VSMVDD]

noise in opamps is usualy caused by high frequency{local crap}
in low freq circuits{audio}

best add filtering to the psu rails close to the chip

then avoid the problems of special design to avoid noise

if your inputs are noise
it is becouse you have NO zero ground referance to the design you made

ie a 100M res from the -+ opto input to ground
to dump noise off the inputs
this is called a balanced referance ground system

and is standard to lf amps