Continue to Site

Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

High speed voltage to current

Status
Not open for further replies.

JulesMhz

Newbie
Joined
Jun 29, 2023
Messages
1
Helped
0
Reputation
0
Reaction score
0
Trophy points
1
Activity points
11
I have a signal oscillating at tens or hundreds of MHz (up to 200 MHz expected), with 2.5 V mean and approx 200 mV peak to peak. I'd like to produce a current proportional to this signal at approx 40-50 mA mean to drive a laser diode.

I'm thinking about using this kind of floating load voltage to current circuit:

k894i.jpg


Is this kind of circuit suitable for up to 200Mhz signal?

If yes, does the AD8000 opamp would be suitable?

If not, which kind of (simple) circuit should I use (I'm running single supply)?

Thank you very much for your help.
 

Basic sim seems to work. Note I did not bias part to yield a
+ only input V. Note I did not have a laser diode model so just used
a small signal diode for sim purposes.

The challenges will be stability at this frequency. I would look at the
manual for the dev board AD sells, paying specific attention top layout
and their specific recommendations for bypass caps.

1688040863645.png


I did a bode plot but do not trust it as my circuit does not have all the parasitics in
it and actual components used. But at 100 Mhz still a lot of G left and phase flattens out
at 80 degrees, so externals phase contribution could bite you in the rear end. Amp has

PSRR at these freq can also cause you a lot of grief :

1688041921109.png




Regards, Dana.
 
Last edited:

"RF over fiber" is a real thing and you can probably find a lot of info
on how people do modulation for linear signals.

While a transconductance amp would fit the theoretical bill, it's liable
to be over-slow.

Laser modulation must be single ended (can't go darker than dark)
so you might find a resistor network that does the job (perhaps a
bias legRbase to +5 for lasing current at half scale, and a CR-Rbase
divider port that gives the right current-for-voltage scaling (this
presumes the 2V input is well lower-Z than the rest of it).
 

Status
Not open for further replies.

Similar threads

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Back
Top