[time-nuts] Opamp Phase noise: OPA653 additional measurements

Azelio Boriani azelio.boriani at screen.it
Tue Apr 17 10:14:24 UTC 2012


Very good. I'm fascinated by the figures... how can such phase noise levels
be measured and, in general, being able to "sense" the most faint signal.

On Tue, Apr 17, 2012 at 11:25 AM, Bruce Griffiths <
bruce.griffiths at xtra.co.nz> wrote:

> Subsequent measurements using an improved technique has allowed the true
> flicker phase noise characteristics of  a pair of OPA653 opamps to be
> determined.
>
> Opamp
>    Gain 1x (6db folled by 6 db attenuator consisting of a 50 ohm resistor
> in series with the output of the opamp and the 50 ohm load resistor)
>    Signal input level: + 10dBm
>
> OFFSET    Opamp PN (dBc/Hz)    Measurement system PN (dBc/Hz)
>
> 1                -148                                -161
>
> 10              -161                                -172
>
> 100            -164                                -177
>
> 1000          -164                                -179
>
> Source: 10MHz low phase noise OCXO removed from a Thunderbolt amplified by
> a QBH9816 amplifier.
>
> Conclusion: FET opamp PN in the flicker region can be quite low despite
> its somewhat higher baseband flicker noise than that of some bipolar input
> opamps.
>
> Bruce
>
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