[Elecraft] Analog vs. Digital Front Ends

[Jim Bolit]

Interesting.
The government is a big driver for wide range receive capabilities / signal analysis, but cost is not the main driver there.
Jim
W6AIM




-------- Original message --------
From: Lyle Johnson <kk7p4dsp at gmail.com>
Date: 9/16/2015  9:40 AM  (GMT-06:00)
To: elecraft at mailman.qth.net
Subject: Re: [Elecraft] Analog vs. Digital Front Ends

One has to ask, "Which large consumer of high dynamic range, high-speed
sampling ADCs is requiring more performance than presently exists?  What
drove the market for the present ones?"

The driver for the current generation, based on limited information, is
the technical requirements for cellular base stations.  Perhaps as we
move from the current generation to the next generation of mobile
devices, we'll see a need arise for better base station performance.

To get another 15 to 18 dB of blocking dynamic range (BDR), we need 3
more effective bits.  This either comes from more bits at conversion
time (a 20-bit high-speed ADC instead of a 16-bit), increasing the
sampling rate dramatically while maintaining the same effective number
of bits (ENOB as it is called in data sheets), or a combination of
both.  And of course you also need the downstream digital devices,
usually field programmable gate arrays (FPGAs) to implement what we
think of as the receiver (oscillators and mixers and filters) that can
handle the required interfaces at the necessary speeds, and the internal
resources to maintain precision).

Until there is a viable market for a large number of such ADCs,
semiconductor manufacturers are unlikely to invest a lot in R and D to
get there.  At this point, they want to compete with each other for the
existing market, so they try to offer incremental advantages over their
competitors.

We may eventually be able to buy ADCs with the required performance to
obtain the BDR many of us want and some of us need, but unless there is
a large demand for the products whose design needs include ADCs that
will provide this performance, there is little incentive for their
development.

My personal opinion only,

Lyle KK7P
>
>> So how long before ADC technology catches up to the K3? If Moore's
>> law applied (doubling of performance every couple years) it wouldn't
>> be long. Unfortunately Moore's law applies mainly to digital
>> circuitry but the key parts of an ADC are analog (the "A" in "ADC").
>> Unless there is a big theoretical breakthrough in ADC architecture, I
>> think we still have some years to wait.
>
> The question really boils down to when will we see affordable high
> voltage ADCs.

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