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

[Bruce Griffiths]

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