Great disassembly job. There's yet another branch of the rabbit hole that Tom almost fell down:
... the multiplier is based on a classic form,
having a translinear core, supported by three
(X, Y, and Z) linearized voltage-to-current
converters, and the load driving output amplifier.
I have no clue how the thing works!
The 'translinear' school of design was founded (or at least popularized) by Barrie Gilbert at Analog Devices (https://en.wikipedia.org/wiki/Translinear_circuit , https://en.wikipedia.org/wiki/Barrie_Gilbert ). Gilbert was one of the undisputed GOATs in the analog field and a full-fledged Renaissance man in his own right. It's worth reading more about him if/when you have the time and inclination.
It would be interesting to benchmark this against consumer USB DACs that are marketed for sound. You can get 32-bit 192kHz bandwidth (384kHz sampling rate) DACs now for under $200. Obviously this is much lower bandwidth than the R&S, but I'd be interested to see the dynamic range of a modern DAC when approaching Nyquist; I don't have a strong belief one way or the other over which would win, given that 14-bits of dynamic range is about where the integrity of your analog path starts to matter a whole lot.
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Sound Blaster claims "up to" 130dB of dynamic range on theirs. Putting aside how much work the "up to" id doing, this would make the last 9 or 10 bits completely useless, even for undithered signals, but I was thinking of something cheaper, by one of those fly-by-night companies with names made of random letters.
I'm amused that it's just a PC motherboard, and that it uses ISA to talk to the generator hardware itself. Makes perfect sense; nothing needs high data rates there, and it's really easy to interface with. I just wouldn't have necessarily predicted it before seeing the case open.
I'm trying really hard not to want to turn this into a dac for my stereo system. They build really nice boxes..
I have a PSL-3 industrial controller (well, two, but one is broken) on the shelf behind me that I'm using for the noble purpose of playing Theme Hospital in Windows 98.
Wonderful article and I don't even know that this device existed perhaps due to Agilent/Keysight bias laboratory/shop.
R & S AMIQ Modulation Generator general specs is available here [1].
Fun facts, the venerable Silicon Valley was started by Hewlett-Packard (HP, then Agilent, now Keysight) that mainly supplying function/signal/waveform generator for the then booming radar and electronics industry.
HP Garage is now a designated landmark and marked with a plaque calling it the "Birthplace of 'Silicon Valley' " [2].
Rohde and Schwarz AMIQ Modulation Generator Teardown
(tomverbeure.github.io)68 points by iamsrp 8 June 2025 | 26 comments
Comments
[edit]
Sound Blaster claims "up to" 130dB of dynamic range on theirs. Putting aside how much work the "up to" id doing, this would make the last 9 or 10 bits completely useless, even for undithered signals, but I was thinking of something cheaper, by one of those fly-by-night companies with names made of random letters.
There are probably only a few electrical engineers in the entire world that actually use this stuff on a day to day basis.
I have a PSL-3 industrial controller (well, two, but one is broken) on the shelf behind me that I'm using for the noble purpose of playing Theme Hospital in Windows 98.
R & S AMIQ Modulation Generator general specs is available here [1].
Fun facts, the venerable Silicon Valley was started by Hewlett-Packard (HP, then Agilent, now Keysight) that mainly supplying function/signal/waveform generator for the then booming radar and electronics industry.
HP Garage is now a designated landmark and marked with a plaque calling it the "Birthplace of 'Silicon Valley' " [2].
[1] Rohde & Schwarz – AMIQ04 I/Q Modulation Generator:
https://testworld.com/product/rohde-schwarz-amiq04-iq-modula...
[2] Hewlett-Packard:
https://en.wikipedia.org/wiki/Hewlett-Packard