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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