Voltage to PWM chip (similar to class D)?

I can design you a chip >:-} ...Jim Thompson

Den torsdag den 29. maj 2014 23.20.26 UTC+2 skrev Joerg:

does it have to be pwm?

not hysteretic, deltasigma or UcD ?

-Lasse

Is it fifty or a thousand ? It makes a difference.

How about a sawtooth or triangle waveform and a comparator. Close a feedback loop around that, with a PWM to DC converter; the PWM-DC part can be made very linear.

Den torsdag den 29. maj 2014 23.53.48 UTC+2 skrev John Larkin:

put loop around integrator,comparator and flipflop and you have deltasigma

cut down to the bone,

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How about a CMOS 555 with a current source to charge the capacitor?

Cheers

Phil Hobbs

This one has to be PWM but we can possible delinearize upfront (possibly ...). Better would be a clean 1:1 PWM.

Sorry, 50kHz to 1000kHz.

That's what I wanted to avoid for real estate reasons. But if I hafta I'll do it.

That could be done but would gradually lead me to the circuit complexity (size) of a comparator solution. Because I'd have to control the current source over a wide range and very precisely.

I was hoping I'd not be the only one needing a precise voltage-to-PWM function.

If you want 0.1% accuracy, you might be able to do it open-loop, with a very linear ramp, but it will be hard at that frequency. If you only want 0.1% resolution ("granularity"?) it's not so bad.

Can you use delta-sigma? There are some integrated d-s modulators around.

I could but then I'd have to build a one-shot that stretches the pulses into a very precise length and that's almost the same kind of challenge as building my own PWM generator (needs too much space).

Hey! Microprocessors are simple! You just need to learn some valuable skills, that's all.

But generating a PWM at 1MHz with a resolution of 0.1% mean you need a base frequency for your counter of 1GHz. I don't know any CPU that could do that.

why would you need a one-shot? the output is clocked

something like the AD7401, if you want to be sure a flipflop on the output

-Lasse

he did say the input was limited to 15KHz, so 2*15K*1000 >= 30MHz

plenty of cpus that can do that

-Lasse

Someone, TI I think, has a ARM with nanosecond-resolution PWM outputs. But Joerg seems to want an analog input.

Digital delay generators generally use a clocked coarse width generator with analog interpolation down to picoseconds. Too complex for this app.

Some MCUs follow the PWM section with a selectable delay line, which gives you sub-clock PWM resolution.

But often you can stand higher error in the higher frequencies than you can at DC. In that case you can put a sigma-delta modulator between your drive number and your PWM. I do this often in control loops, because it works well, it's easy, and it's cheap.

Yeah, have a tube of those 1 cell voltage capable Cmos versions. They don't handle the upper voltage well but they sure do work well in one cell applications.

Jamie