3 discusses benefit of Q=100 bandpass at 25Hz
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Here is an OpAmp design, using 1 nanoVolt noise density OpAmps, in Avcl= 60dB and 100dB; stage 1 is DC coupled, to avoid huge capacitors (vulnerable to Efield interference); stage 2 is DC-blocked in the gain-set network; for fun, I've included 10 millivolts of PowerSupply interference in each OpAmp. Result? the SNR is -70dB. Vout is 29milliVolts; thermal noise is 1 volt; power supply noise is 93 volts. [Without power supply ripple, SNR is -31.5 dB]

enter image description here

And here is why the PowerSupply trash comes through so strongly: the OpAmp PSRR is only 80dB (default values) AND the LsRsCs on OpAmp VDD have no impact on 60/120 ripple (the Caps need to be much bigger, and the series Rs at least 10X bigger).

enter image description here

Now add the benefit of a Lockon Amplifer: modeled as 25Hertz bandpass, with Q=100. The SNR improves (with 1nanoVoltPP input) from -30dB to -5dB. Note, in upper right, I clicked off the "Gargoyles" and "PSI". Note also, below SNR/ENOB windows, I set the FOI FrequencyOfInterest value to exactly 25Hz, necessary because of the highQ filter. And I used the LowPass Filter LRC stage, so I could place the LC resonance exactly at 25.00Hz, using the worksheet; at Q=100 this is necessary. enter image description here

Here is the noise plot, covering 24 to 26Hz. Notice the many noise sources listed on righthand side, but only the Amplifier Noise and Rg are important. Rg is the 10.01 Ohms to ground, setting the 60dB gain of that Buffered Gain Follower. Again, the Rnoise of the first opamp is 62_ohms, or 1.0nv/rtHz. enter image description here

Here is an OpAmp design, using 1 nanoVolt noise density OpAmps, in Avcl= 60dB and 100dB; stage 1 is DC coupled, to avoid huge capacitors (vulnerable to Efield interference); stage 2 is DC-blocked in the gain-set network; for fun, I've included 10 millivolts of PowerSupply interference in each OpAmp. Result? the SNR is -70dB. Vout is 29milliVolts; thermal noise is 1 volt; power supply noise is 93 volts. [Without power supply ripple, SNR is -31.5 dB]

enter image description here

And here is why the PowerSupply trash comes through so strongly: the OpAmp PSRR is only 80dB (default values) AND the LsRsCs on OpAmp VDD have no impact on 60/120 ripple (the Caps need to be much bigger, and the series Rs at least 10X bigger).

enter image description here

Here is an OpAmp design, using 1 nanoVolt noise density OpAmps, in Avcl= 60dB and 100dB; stage 1 is DC coupled, to avoid huge capacitors (vulnerable to Efield interference); stage 2 is DC-blocked in the gain-set network; for fun, I've included 10 millivolts of PowerSupply interference in each OpAmp. Result? the SNR is -70dB. Vout is 29milliVolts; thermal noise is 1 volt; power supply noise is 93 volts. [Without power supply ripple, SNR is -31.5 dB]

enter image description here

And here is why the PowerSupply trash comes through so strongly: the OpAmp PSRR is only 80dB (default values) AND the LsRsCs on OpAmp VDD have no impact on 60/120 ripple (the Caps need to be much bigger, and the series Rs at least 10X bigger).

enter image description here

Now add the benefit of a Lockon Amplifer: modeled as 25Hertz bandpass, with Q=100. The SNR improves (with 1nanoVoltPP input) from -30dB to -5dB. Note, in upper right, I clicked off the "Gargoyles" and "PSI". Note also, below SNR/ENOB windows, I set the FOI FrequencyOfInterest value to exactly 25Hz, necessary because of the highQ filter. And I used the LowPass Filter LRC stage, so I could place the LC resonance exactly at 25.00Hz, using the worksheet; at Q=100 this is necessary. enter image description here

Here is the noise plot, covering 24 to 26Hz. Notice the many noise sources listed on righthand side, but only the Amplifier Noise and Rg are important. Rg is the 10.01 Ohms to ground, setting the 60dB gain of that Buffered Gain Follower. Again, the Rnoise of the first opamp is 62_ohms, or 1.0nv/rtHz. enter image description here

2 added 70 characters in body
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Here is an OpAmp design, using 1 nanoVolt noise density OpAmps, in Avcl= 60dB and 100dB; stage 1 is DC coupled, to avoid huge capacitors (vulnerable to Efield interference); stage 2 is DC-blocked in the gain-set network; for fun, I've included 10 millivolts of PowerSupply interference in each OpAmp.

  Result? the SNR is -70dB. Vout is 29milliVolts; thermal noise is 1 volt; power supply noise is 93 volts. [Without power supply ripple, SNR is -31.5 dB]

enter image description here

And here is why the PowerSupply trash comes through so strongly: the OpAmp PSRR is only 80dB (default values) AND the LsRsCs on OpAmp VDD have no impact on 60/120 ripple (the Caps need to be much bigger, and the series Rs at least 10X bigger).

enter image description here

Here is an OpAmp design, using 1 nanoVolt noise density OpAmps, in Avcl= 60dB and 100dB; stage 1 is DC coupled, to avoid huge capacitors (vulnerable to Efield interference); stage 2 is DC-blocked in the gain-set network; for fun, I've included 10 millivolts of PowerSupply interference in each OpAmp.

  Vout is 29milliVolts; thermal noise is 1 volt; power supply noise is 93 volts.

enter image description here

And here is why the PowerSupply trash comes through so strongly: the OpAmp PSRR is only 80dB (default values) AND the LsRsCs on OpAmp VDD have no impact on 60/120 ripple (the Caps need to be much bigger, and the series Rs at least 10X bigger).

enter image description here

Here is an OpAmp design, using 1 nanoVolt noise density OpAmps, in Avcl= 60dB and 100dB; stage 1 is DC coupled, to avoid huge capacitors (vulnerable to Efield interference); stage 2 is DC-blocked in the gain-set network; for fun, I've included 10 millivolts of PowerSupply interference in each OpAmp. Result? the SNR is -70dB. Vout is 29milliVolts; thermal noise is 1 volt; power supply noise is 93 volts. [Without power supply ripple, SNR is -31.5 dB]

enter image description here

And here is why the PowerSupply trash comes through so strongly: the OpAmp PSRR is only 80dB (default values) AND the LsRsCs on OpAmp VDD have no impact on 60/120 ripple (the Caps need to be much bigger, and the series Rs at least 10X bigger).

enter image description here

1
source | link

Here is an OpAmp design, using 1 nanoVolt noise density OpAmps, in Avcl= 60dB and 100dB; stage 1 is DC coupled, to avoid huge capacitors (vulnerable to Efield interference); stage 2 is DC-blocked in the gain-set network; for fun, I've included 10 millivolts of PowerSupply interference in each OpAmp.

Vout is 29milliVolts; thermal noise is 1 volt; power supply noise is 93 volts.

enter image description here

And here is why the PowerSupply trash comes through so strongly: the OpAmp PSRR is only 80dB (default values) AND the LsRsCs on OpAmp VDD have no impact on 60/120 ripple (the Caps need to be much bigger, and the series Rs at least 10X bigger).

enter image description here