[HN Gopher] Radio Architecture Matters: A Review of RF Sampling ...
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Radio Architecture Matters: A Review of RF Sampling vs. Zero-IF
Author : teleforce
Score : 37 points
Date : 2023-12-07 11:54 UTC (1 days ago)
(HTM) web link (www.analog.com)
(TXT) w3m dump (www.analog.com)
| jhoechtl wrote:
| While this article is about frequencies you typically use in Wifi
| communication, it touches another point.
|
| I am a ham radio operator and with many radio devices delivered
| these days I witness the following. Mostly high quality
| components are used but they are assembled in a way that lacks
| knowledge of harmonics, interference, cross-talk, parasitic
| effects in general. PC board design makes it obvious and results
| in a sub-quality end product.
|
| It seems like a basic engineering craft which got lost in the
| last 30 years.
| willis936 wrote:
| I don't consider RF PCB layout basic engineering and I don't
| think it's lost. Plenty of us EEs have read Pozar and could
| make a competent RF layout given time and resources. I'd first
| guess that bad layouts are a management decision.
| felipemnoa wrote:
| This pozar?
|
| https://www.amazon.com/Microwave-Engineering-David-M-
| Pozar/d...
| mwbajor wrote:
| Yes. But if you really want to get into it you need to do
| it. You could make some cheap PCBs and measure them with a
| cheap network analyzer. RF design has never been more
| accessible. The books will get you started and you will
| start to think about things like de-embedding circuit
| elements which is very important and not covered in books.
| You will also start to see why people consider RF design
| challenging; e.g. curves in the books will depict a "trend"
| in the circuit and in real-life, everything is a capacitor
| and/or inductor which causes the real life measurements to
| deviate substantially from the ideal for reasons that are
| not always obvious.
|
| An even more cheaper accessible intro to RF is just plain
| old analog electronics. Building amplifiers ,etc.
| lb1lf wrote:
| I'd upvote this ten times if I could.
|
| I had the good fortune of being exposed to both Pozar, an
| excellent lecturer and a wizard of an RF lab postdoc when
| studying RF engineering, and the utility of simply
| spending lots and lots of time in the lab, trying all
| sorts of implementations of filters, transmission lines,
| antennas and whatever caught our fancy, prototyping with
| wild abandon, verifying (or getting stymied by) the
| results, refining our measurement skills along the way...
|
| Priceless.
|
| Then all RF design jobs disappeared overnight and I ended
| up doing PLC coding instead of working with radio - but,
| hey, University was great fun, and RF design definitely
| is one of the fields where there's still room for
| intuition and a bit of artistry in addition to just
| knowing the hard theory of the subject.
| edrxty wrote:
| Where are all the jobs going? There are a lot of RF
| things going on at an ever increasing pace but I don't
| see a lot of people hiring in the field. Do all the
| defense primes just have a silo of gray beards they keep
| in a dungeon somewhere?
| mwbajor wrote:
| Yes. Many analog design groups in college went from 10's
| of students 10-15 years ago to just a few now, not due to
| lack of funding but due to a lack of interest. Our
| interface to nature is through analog signals but due to
| the heavy reliance on HW intuition and its relative
| inflexibility (but more 'elegant solutions' if you ask
| me) analog electronics continues to grow in unpopularity
| in industry and academia follows. Yes, there are just
| some older guys updating old designs in many instances.
| The push for RFSOCs and similar products is partially to
| reduce reliance on the greybeards. Its a shame because
| there are very interesting areas of analog electronics
| such as continuous time signal processing.
|
| TLDR: To answer your question, to reduce the reliance on
| a relative few engineers, the market solved it with a few
| products that are 'just good enough'. This has become a
| self perpetuating cycle, race to the bottom. There will
| still be many analog/RF EEs but relegated to a few niche
| sub-industries serving mainly the DoD and RFIC
| industries. Even the telecom industry is planning to pipe
| back raw, downconverted baseband data to a central
| location to do SDR DSP rather than rely on a modem at the
| basestation. All for flexibility in lieu of
| power/efficiency, NRE etc.
| willis936 wrote:
| You aren't painting a fair picture. RFSoCs cost more but
| they also have _much_ more dynamic range (both amplitude
| and temporal). It 's just just about configurability, but
| also performance.
| mwbajor wrote:
| As I said, nature is analog, it will never go away.
| Interesting areas of analog research are in things such
| as switched capacitor architectures where you can filter
| as close to the antenna as possible, reducing the impact
| of an interferer on the rest of your signal chain. Also
| similar is continuous time signal processing where you
| can perform your signal processing on an analog signal
| without discretizing it in time, effectively giving you
| the ability to make sense out of your analog data as
| close to the sensor (or antenna) as possible.
|
| The problem is you can't tweak these things with a
| software update. Their relative inflexibility makes them
| unpopular outside of a defense or research setting but
| analog solutions are typically higher in performance than
| digital solutions but that can depend on definition as
| well.
| felipemnoa wrote:
| Thank You! This is really good advice. Just wish I had
| the time to really get into it.
| gorkish wrote:
| > bad layouts are a management decision.
|
| That's an interesting way to describe AliExpress shovelware,
| but OK, yeah it's a "management decision"
| willis936 wrote:
| Management chooses to make and sell a bad product. It's not
| that RF design is somehow arcane wizardry lost to time.
| gorkish wrote:
| Oh god, the receivers being shipped with the LTC2208! They do
| not even deserve to have supply of that chip. What a
| disservice.
| edrxty wrote:
| Can you expand on this? You have my interest...
| cozzyd wrote:
| Analog pushing back against "fuck it, let's use an RFSoC" ?
| spacecadet wrote:
| Not push back to me. As an "analog", I love SDR-SOC but what
| this is saying is that people may lack a fundamental knowledge
| when designing hardware devices that is contributing to these
| challenges.
|
| Id also push back against the article in the sense that I think
| the industry shot itself in the foot trying to provide too many
| options that all overlap. But, I do agree with the sense that
| minimizing the radio architecture to only what it needs to
| operate is smart.
| mwbajor wrote:
| Not only that, but it also stems from "management" or
| "customers" unable to contemplate tradeoffs in the design.
| The reason FPGAs and RFSOCs are pushed so much in certain
| industries (we all know which one) is because the customer
| wants everything reconfigurable because they can't make
| decisions now, or in most cases, not competent enough to make
| decisions now. However, they are OK with buying a $25K+ FPGA
| or RFSOC which is why the market is there and also why few
| understand the actual art of RF design and radio architecture
| anymore. RF budgeting is almost non-existant. Most Jr.
| engineers have never seen a level diagram and the only places
| you will find them is in old watkins johnson app notes. SDR
| design is ultimately a race to the bottom in most cases in
| terms of good design but not necessarily cheap design.
| cushychicken wrote:
| Man I love ADI's tech notes.
|
| They're some of the best in the business at technical marketing.
| Scene_Cast2 wrote:
| Here's a super crude ELI5, feel free to correct me.
|
| Signals crash course: Radio comms have a channel they need to fit
| into (let's say 1.1GHz - 1.2GHz as an example). This means that
| what you send over the air is basically a high frequency
| (~1.15GHz) sine wave. You encode data by slowly varying this sine
| wave (amplitude and/or frequency). The variations are going to be
| super slow, as fast changes in either amplitude or frequency will
| make your signal go outside the frequency limits. It's only the
| sine wave (aka the "carrier frequency") that's high frequency
| (1.15GHz in our case).
|
| There are several ways to digitize this signal. You can do
| "direct RF sampling" - you need a very high sampling rate
| (2.4GHz+ due to Nyquist in our case) and just sample the high
| frequency signal. You can multiply (in analog domain) the RF
| signal from the antenna by another frequency to keep all the slow
| changes but change the carrier frequency. This means that you
| don't need such a high lower sampling rate (you can get away with
| much less than GHz). If your new carrier frequency is just some
| low but non-zero frequency, that's super-heterodyne (IF). If it's
| zero, that's Zero-IF.
| mwbajor wrote:
| Yes all correct, you didn't capture any of the tradeoffs but
| thats the basic idea.
| gorkish wrote:
| Just have to say this is the first time I've seen someone
| introduce the concept of an RF mixer "backwards".
| kurthr wrote:
| I was surprised they didn't use the word homodyne.
|
| One issue they didn't mention, but probably shows up in the
| noise figures is that homodyne receivers suffer from 1/f noise
| in the relatively wide band "direct conversion" amplifiers. Of
| course all of the heterodyne receivers suffer from 1/f up-
| conversion at the mixer.
| teleforce wrote:
| It is rather a soup of terminologies namely homodyne, zero-
| IF, and direct conversion architecture are all referring to
| the same thing.
|
| It seems they are now settling on RF sampling for the newer
| transciever architecture technology but sometime direct RF is
| also being used for example this latter terminology is
| referred by Intel for their new line of FPGA and RF
| transceivers product integration.
| ipdashc wrote:
| This is the first time I've seen it explained like this, and
| having struggled with these concepts in the past, I found your
| explanation really easy to understand. Thanks!
| spr-alex wrote:
| I am looking for PCB designers with RF experience. If this is
| what you're good at, please reach out
| teleforce wrote:
| For both RF sampling and Zero-IF the two of the most popular
| analog manufacturers are TI and Analog Devices.
|
| It's rather intriguing that for RF sampling technology, Intel has
| recently join the bandwagon and called it a game changing
| technology when the RF sampling is integrated with high speed
| FPGA [1].
|
| Intel Delivers a Game-Changing, Analog-Enabled Direct RF FPGA
| Portfolio:
|
| https://community.intel.com/t5/Blogs/Products-and-Solutions/...
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