Re: About TIAs

john larkin <JL@gct.com> wrote:

On Fri, 27 Dec 2024 14:14:31 -0000 (UTC), Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:
 

Jan Panteltje <alien@comet.invalid> wrote:

https://www.electronicdesign.com/technologies/analog/article/55250719/phlux-technology-tailoring-the-design-of-transimpedance-amplifiers-to-infrared-sensor-apps-part-2
 
I just drive the photo diode directly into the base of an NPN .....
(ducks).
 

 
That’s basically a homebrew phototransistor, and may work great for
applications that don’t require high speed, low noise, or accurate
calibration. (There are lots of those.)
 
A slightly more advanced method is to replace the NPN with a cheap MMIC
amplifier. If you have at least a milliamp of photocurrent, that’ll get you
close to the shot noise, and it’ll be pretty fast unless the PD itself is
slow.
 
We sell fancier photoreceivers for much dimmer light, where it’s more
difficult to preserve both low noise and wide bandwidth.
 
Cheers
 
Phil Hobbs

 
MMICs are. But be aware
that some, the newer self-biasing kind, get very weird at low
frequencies, and the data sheets hide it.

Yeah, you wind up fighting the bias FB loop, which doesn’t end well.

Speaking of “fabulous, fast, low noise, stable, and cheap,” Simon and I
built a < 60-ps TDR, honest 10%-90%, with nice clean edges and no artifacts
to speak of.

 Including a dual 16-bit DAC to set thresholds for the Rx andTx pulsers, a
quad 8-bit to set the beginning and ending voltages of the ramp, an LPC845
MCU, board, SMA connectors, the fully stuffed boards are $16 in quantity
25.

The same 24-inch RG188 patch cord also measures about 60 ps with an SD-24,
so the TDR may be better than that.

Alpha waves emanating. ;)

Cheers

Phil Hobbs


--
Dr Philip C D Hobbs  Principal Consultant  ElectroOptical Innovations LLC /
Hobbs ElectroOptics  Optics, Electro-optics, Photonics, Analog Electronics