CHARLES HUTTON wrote:
> By the way, there are some 18 bit ADC's with spurious free dynamic range in
> excess of 103 dB and sampling rates of over 1 MSPS. For 455 kHz IF's, they
> would provide a fine A/D conversion that should meet even our most demanding
> needs.
Spurious-free dynamic range has to be referenced to a measurement noise
bandwidth to have any meaning because dynamic range is measured against a noise
floor. Furthermore SFDR varies nonlinearly with noise bandwidth because we are
dealing with nonlinearities. If the 103 dB SFDR is referenced to 1 Hz (which
is common practice for many systems and components), then the SFDR would
degrade to 63 dB when measured in a 100 Hz noise bandwidth if the dominant
nonlinearity is third-order. That 63 dB now seems less appealing as a dynamic
range figure.
73, John W1FV
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