ARB Hi Current tool

[JonW]

Alright chaps

I recently needed to return to Diseqc (pulsed 22kHz) over coax plus DC and redesign a transceiver onto a cheap SOT23-6 MCU.  Testing is extensive as there are so many products on the market that don't comply with the Eutlesat specs, so the protocol is complicated and has to capture everything.  The issue I had was that I needed to modulate a moderately high current PSU with all kinds of waveforms and alter the amplitude-frequency and mark/space ratio, plus add wideband noise or DC-DC ripple on top, have it fast, wideband with an accurate linear, fine resolution, DC offset.  I purchased a DG922 Pro Arb (a lovely bit of kit for the money) as this is dual channel and very flexible, but like all other Arbs or waveform generators, the output drive (impedance) is relatively high, so driving up to 1A at 20V just can't be done.
Long story short, I have designed a 24V 1.5A dual-channel waveform buffer with the following features

•    External DC Ref in per channel  0 to 5V ( Gain of 5) to achieve 0 – 25V (limited by Drive IC to +23V)
•    Internal DC Ref per channel  0 to 5V ( Gain of 5) to achieve 0 – 25V. This channel is driven by a digital pot that gives a resolution of 100mV after a very linear amplification, giving 0.1V to 23V in 100mV increments.
•    2 x External AC inputs (Gain typically -2) bandwidth 10Hz to >20MHz (Flat response)
o    Can super impose 2 Channels of AC/noise
o    Need to test 3dB BW but think it will be around 30MHz
•    High isolation 200MHz front-end switch for OOK modulation per channel
o    Gate the input modulation (Can have Dual input control)
o    Connected to the PWM pins on MCU so you can use HW PWM or drive manually
•    1.5A max current per channel (user needs to manually adjust Drive amp VCC headroom to minimise power dissipation).  I run this from a bench PSU but may add a tracking DC-DC converter in future
-    Can combine both outputs to increase current (thermal limitations apply)
•    External NCO output (DC to 32MHz 5V)
o    This output can also be used to trigger the ARB for other modulations
o    General purpose I/O
•    Temperature monitoring of each drive IC via MCU
•    Programmable Current Limiting via MCU
•    Digital On-off control of output via MCU
•    USB-C controlled with Bootloader
•    External DC input
•    Slew Rate >25V/us
•    3 Switches, 6 LEDs
•    <10mV Pk-Pk noise output (DC only)
•    Runs on Positron Basic so it is a breeze to customise

Currently building libraries to drive everything. 

I only had a day to design, simulate and lay it out, so there may be other features that could be useful to others but I did include features so one can measure PSRR or gate the input modulation frequency and have the ability to change the DC offset to emulate noisy DC-DC converters or transients on the DC supply.  Adding the MCU and bootloader with input and output control, plus the Digitpot, makes this pretty unique test board.  I did find one similar product in the USA, but these are a few thousand dollars, single channel, single input, <1MHz BW and no external MCU or PC control.

I am just testing it now, and it's working perfectly. It got me thinking that there must be thousands of use cases for Audio/PSU/Production test/PSU emulation/PSU testing/Stepped Digital Programmable PSU. If there is interest, I may look at selling it in the future. 
I mean it is not a sub $50 product as it has a lot of high-end parts and BNC but is way less cost and more powerful than anything else I have seen on the market

Pic attached, feel free to comment

[JonW]

John and Les.
Can make a decent high linearity transmitter from 10Hz to 25MHz, ultra broadband as output Z is constant low impedance so can be resistively matched easily. Dual channel so could also do passive doppler ranging as the phase is controlled and programmable so can steer the beam in azimuth. See lots of so called passive radar projects.
Could easily expand to 2^n units and digitally track phase and and amplitude to combine at high power. Just wondering if you could build a massive Mimo rig and duct (beam steer) at HF .. food for thought

Need a big garden.. or lower the frequency and use ham friternity in a city or town to make a massive phased array. Can control phase and amplitude,  so distance vs frequency can  be compensated by wavelength  to build a phased array, can easily phase sink via Internet or GPS...
With MCU driving both channels you can control the modulation amplitude and phase so have  the ultimate      I and Q.. ( plus 2 resistors for phase combiner ), then anything possible.

[JonW]

I worked on the code for this over the weekend and thought I would share a screenshot. This is a single-channel ramped voltage controlled from the PIC, working into a 1A active load. I have added a feature where the user can load a script into flash memory from a terminal to control the voltage and delays to precise timings in 100mV steps, thus creating a fast Arb-like function with minimal effort and 1000's instructions long.  Ramp dv/dt can also be adjusted to control the ramp rate