Bruce wrote:
Your statement about the PN of comparators conflicts with my
measurements. The LTC6957 evaluation board had an 18dBc/Hz lower
phase noise floor than a comparator circuit with 10MHz 15dBm inputs.
However I only measured a single comparator circuit. The Holzworth
sine to CMOS converter had a comparable PN to the LTC6957-4.
I haven't, as yet measured the PN of an optimised Wenzel circuit.My
setup for this measurement had a PN floor of around -180dBc/Hz.
There are many, many ways of getting unnecessarily poor PN
performance from comparators (including Wenzel-style squarers) -- one
has to make sure not to make any of myriad mistakes in both design
and execution. You didn't say which comparator you tried, or in what
circuit, so I'm not in a position to suggest things to check (or to
confirm that the comparator you tried performs similarly poorly in my
tests, if that is the case).
One sanity check you can try -- disable the filtering on your 6957
eval board. According to the LT data presented in the chart I
posted, which agrees very closely with my test results, at
10MHz/15dBm there should be essentially no change in the PN compared
to the results you obtained with filtering enabled. If you see a
significant difference, then something is causing anomalous results.
Best regards,
Charles
ps. You often respond to one message by replying to a different
message, as you did in this case. It would be helpful for someone
who just joins a thread, and for continuity in general, if you would
reply to the message to which you are actually responding. That way,
readers who are new to the thread will have the context they need,
and your interlocutor will have his or her previous message
conveniently available to refer to in any further message.
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