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igs noise of NMOS in 65nm

naderi

Hi all,

Noise analysis of a differential amplifier, which is in right OP, shows the noise due to igs and igd is even higher than fliker noise at 1kHz.

spectrum of the noises (igs and igd) is proportional to 1/f^2.

 Device                   Param    Noise Contribution    % Of Total
/Iint1/Iopamp/M1inp      igs      1.07235e-13           25.51
/Iint1/Iopamp/M1inn      igs      1.03778e-13           24.69
/Iint1/Iopamp/M1inp      igd      9.57556e-14           22.78
/Iint1/Iopamp/M1inn      igd      9.2761e-14            22.07
/Iint1/Iopamp/Mpload1    fn       3.9511e-15            0.94
/Iint1/Iopamp/Mpload2    fn       3.80531e-15           0.91

However, igs=183 fA and igd=-4 fA in /Iint1/Iopamp/M1inp
How comes such a small gate currents produce that much noise?

Any ideas?

Thanks,

PS. I am using 65nm CMOS tech using BSIM4 models

  • Presumably there's a lot of gain from that current to the output of the circuit? Note that the noise summary gives the output referred noise, rather than the noise at the noise source.

    Andrew.

  • Thanks Andrew,

     The gain is about 100, but the problem is that why igd/igs noise is more than 25 times larger than flicker noise. This is given at 1kHz, and at lower frequesncies it is even higher. Such a large noise does not make any sense from that small gate current.

     

    Have you seen any equation for igs noise in books or papers? If someone have an equation it would help to undrestand what is going on. I have studied BISIM4 modling, but could not find an equation with 1/f^2 characteristics.

     

    Regards,

    Ali

  • Maybe you should log a service request on this so somebody can take a look in more detail (I'm a bit short of time at the moment due to work commitments - as you know, the Cadence folks here respond in their spare time). Looking at the bsim documentation at Berkeley might help.

    Andrew. 

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