[Premium-Rx] The new R&S EM510 Direct-Sampling HF Receiver

[Pieter Ibelings]

There is no 24 bit ADC running at 80 MHz. Current state of the art is 16-18 
bits running at that speed. There are some military parallel ADCs that use 
16 bit parts that are averaged to get some extra bits. At some point, more 
bits does not buy you anything. For example,

if you have an ADC that has an ENOB of 18 bits at 80 MS/s, that is 
equivalent to a signal to noise of 110dB in a nyquist band. If this ADC has 
a full scale of 10dBm then the noise per Hz will be:

+10dBm - 110dB - 10* Log(40,000,000Hz) = -176dBm/Hz

This is already below the noise floor. At this time, the thermal noise 
dominates the low end of the ADC. In order to improve the dynamic range, you 
need to start moving the high end of the ADC up as in increasing the full 
scale signal (clipping level).

This is a reason why I know that R&S does not have such a part. If the noise 
per Hz is lower than the -174dBm/Hz then it would still read -174dBm/Hz at 
room temperature. This is  equivalent to having an amplifier with less than 
0dB noise figure.

There are some lower frequency parts that have much higher resolutions. 
These could be used in an I/Q type receiver with an ADC on both quadrature 
outputs.

Pieter, N4IP

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