From: jl@glen--canyon.com   
      
   On Thu, 29 Jan 2026 13:01:31 -0500, Phil Hobbs   
    wrote:   
      
   >Hi, all,   
   >   
   >I'm doing a high-accuracy version of the laser noise canceller   
   >.   
   >   
   >In particular, to get better cancellation accuracy, I want to get rid of   
   >the input offset voltages of a couple of op amps.   
   >   
   >One approach to this is to use a chopamp integrator to snoop the summing   
   >junction, and dork the noninverting input to force the summing junction   
   >to average 0.00000V.   
   >   
   >This is nice conceptually, but there are a couple of worries:   
   >   
   >1. Chopamps kick out nasty switching spikes, which will have to be   
   >decoupled sufficiently well.   
   >   
   >2. Weird-ass composite amplifiers always have weird settling behavior.   
   >   
   >I haven't done this lately, but I'm thinking of a TLV2333.   
   >   
   >Any wisdom?   
   >   
   >Thanks   
   >   
   >Phil Hobbs   
      
   Would the Johnson noise of a resistor wreck the input, like if you   
   lowpass filter the summing junction into the offset servo?   
      
   Can you do anything useful with the other end of the photodiode? Seems   
   a shame to waste that current.   
      
   I just finished a 4-layer double-sided-parts pcb layout and discovered   
   that I forgot to include the threshold generator circuit. I can   
   squeeze in the parts somewhere but routing will be nasty.   
      
      
   John Larkin   
   Highland Tech Glen Canyon Design Center   
   Lunatic Fringe Electronics   
      
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