In Reply to: Re: Motsenbacher and Fitchen "Low Noise Electronic Design" posted by Dan Banquer on August 21, 2006 at 18:05:06:
They were comparing a circuit having no feedback with the exact same circuit with feedback. The equivalent input noise (squared per Hertz) parameter basically takes the mean-square Volts per Hertz (voltage spectral density) value at the output and divides it by the magnitude squared of the voltage gain. This reflects the output noise back to the input, giving a mean-square Volts per Hertz equivalent input noise.So with no feedback, you have a high output noise, but also a high gain. With feedback applied, the output noise is lower because the gain is correspondingly lower. But when you divide the output noise by the gain, it all comes out in the wash to the same equivalent input noise, assuming the contribution of the feedback resistors to the total noise is negligible.
So if the non-feedback circuit had high noise, it was probably a topology-related issue rather than the absence of feedback per se that was causing the problem.
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Follow Ups
- Re: Motsenbacher and Fitchen "Low Noise Electronic Design" - andy_c 18:31:42 08/21/06 (21)
- Re: Motsenbacher and Fitchen "Low Noise Electronic Design" - PAMP 16:14:13 09/03/06 (0)
- Re: Motsenbacher and Fitchen "Low Noise Electronic Design" - Dan Banquer 04:34:17 08/22/06 (0)
- Re: Motsenbacher and Fitchen "Low Noise Electronic Design" - Mahatma Kane Jeeves 18:54:08 08/21/06 (18)
- Re: Motsenbacher and Fitchen "Low Noise Electronic Design" - andy_c 19:11:42 08/21/06 (17)
- Re: Motsenbacher and Fitchen "Low Noise Electronic Design" - Mahatma Kane Jeeves 19:13:17 08/21/06 (16)
- Re: Motsenbacher and Fitchen "Low Noise Electronic Design" - john curl 21:57:14 08/21/06 (15)
- OT: feedback resistors in PAs - Jacques 03:41:40 08/22/06 (14)
- Re: OT: feedback resistors in PAs - john curl 06:24:00 08/22/06 (3)
- Re: OT: feedback resistors in PAs - john curl 09:58:29 08/22/06 (0)
- The 100 ohms resistor... - Jacques 06:56:23 08/22/06 (1)
- Re: The 100 ohms resistor... - john curl 00:52:14 08/23/06 (0)
- Re: OT: feedback resistors in PAs - jneutron 06:12:15 08/22/06 (8)
- Re: OT: feedback resistors in PAs - Jacques 06:48:41 08/22/06 (7)
- Re: OT: feedback resistors in PAs - jneutron 07:16:53 08/22/06 (6)
- Re: OT: feedback resistors in PAs - john curl 15:56:04 08/22/06 (2)
- Ah, forgot to say, you are correct..I used haversine incorrectly..thanks..nt - jneutron 07:13:18 08/23/06 (0)
- Re: OT: feedback resistors in PAs - jneutron 06:43:00 08/23/06 (0)
- You're so quick in calculations... - Jacques 07:50:31 08/22/06 (2)
- Re: You're so quick in calculations... - jneutron 08:09:19 08/22/06 (1)
- BTW, that calculation.. - jneutron 08:21:18 08/22/06 (0)
- Re: OT: feedback resistors in PAs - Dan Banquer 05:00:32 08/22/06 (0)