I'll try shielding from air currents (usually effective to a little
below 1Hz).
The Opamp is thermally connected (metal tab under package is soldered
to) to one of the power planes so the thermal time constant is a little
longer than it would otherwise be.
Bruce
Bob Camp wrote:
Hi
My *guess* is that your 1Hz data may be as much from ambient changes as from
the op amps themselves. No data to back that up on these specific parts, just a
guess.
Bob
On Apr 17, 2012, at 7:28 AM, Bruce Griffiths wrote:
Not yet, I just used the pair of TI evaluation boards which I obtained for
another project.
I intend to mount the various components (splitters, 180 degree hybrids etc) on
a thick aluminium plate to improve the mechanical and thermal stability of the
system.
Bruce
Bob Camp wrote:
Hi
Did you do any temperature stabilization on the op amps?
Bob
On Apr 17, 2012, at 5:25 AM, Bruce Griffiths 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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