So I'm trying to make a model of my spad, It's a reversed biased photodiod e biased (about 10 V) above the avalanche break down voltage. (about 120V) When a photon hits the spad (or from dark counts) I get a fast pulse that discharges the ~2pF of spad capacitance. I measure those pulses. Here's a 'scope shot of pulse with 500k ohm quench R and 500 ohm sense R
spad HV---R_quench----|to fast opamp or x10 scope probe.
And now my spice file... I disconnected the spad from the comparator... so my model is a switch, 100V of back voltage and a capacitor. The pulses have a long ~1us tail as the
2 pF recharges from the 500 k ohm quench R. I don't know why I don't see this in my 'real' spad.First here's a drop box link to the file
Any ideas? TIA George H.
Version 4 SHEET 1 1620 832 WIRE -128 160 -240 160 WIRE 0 160 -32 160 WIRE 96 160 80 160 WIRE 208 160 96 160 WIRE 304 160 208 160 WIRE 464 160 304 160 WIRE -240 176 -240 160 WIRE 304 176 304 160 WIRE 96 208 96 160 WIRE 96 208 -48 208 WIRE 208 224 208 160 WIRE 96 256 96 208 WIRE 464 256 464 224 WIRE -240 272 -240 256 WIRE 304 272 304 256 WIRE 304 272 272 272 WIRE -432 352 -640 352 WIRE -288 352 -384 352 WIRE 96 352 96 336 WIRE 96 352 -288 352 WIRE 208 352 208 320 WIRE 208 352 96 352 WIRE -432 368 -432 352 WIRE 400 400 400 352 WIRE -288 416 -288 352 WIRE -624 432 -640 432 WIRE -432 432 -432 416 WIRE -432 432 -624 432 WIRE 304 432 304 272 WIRE -384 448 -384 432 WIRE -624 464 -624 432 WIRE 400 480 368 480 WIRE -160 512 -208 512 WIRE -64 512 -80 512 WIRE 400 512 400 480 WIRE -384 544 -384 528 WIRE -288 544 -288 480 WIRE -288 544 -384 544 WIRE -208 544 -208 512 WIRE 0 544 0 480 WIRE -64 576 -64 512 WIRE -32 576 -64 576 WIRE 128 576 48 576 WIRE 144 576 128 576 WIRE -384 608 -384 544 WIRE -288 608 -384 608 WIRE -160 608 -160 512 WIRE -32 608 -80 608 WIRE 176 608 48 608 WIRE 304 608 304 528 WIRE 304 608 256 608 WIRE 400 624 400 592 WIRE -384 656 -384 608 WIRE 0 656 0 640 WIRE 16 656 16 640 WIRE 16 656 0 656 WIRE 16 672 16 656 WIRE -384 768 -384 736 WIRE -16 752 -16 640 WIRE 32 752 -16 752 WIRE 128 752 112 752 WIRE 128 768 128 752 WIRE 528 768 512 768 WIRE 624 768 608 768 WIRE 624 784 624 768 FLAG -240 272 0 FLAG 640 640 0 FLAG -208 544 0 FLAG -384 768 0 FLAG 464 256 0 FLAG 400 624 0 FLAG 128 576 Vout FLAG 16 672 0 FLAG 624 784 0 FLAG 128 768 0 FLAG 512 768 Vc FLAG 0 480 Vc FLAG 400 352 Vc FLAG -624 464 0 FLAG 176 688 Vc FLAG -288 608 Vin SYMBOL nmos -128 208 R270 WINDOW 0 -25 37 VRight 2 WINDOW 3 72 -23 VRight 2 SYMATTR InstName Q2 SYMATTR Value LND150 SYMBOL voltage -240 160 R0 WINDOW 0 -61 6 Left 2 WINDOW 3 -93 48 Left 2 WINDOW 123 0 0 Left 2 WINDOW 39 0 0 Left 2 SYMATTR InstName V1 SYMATTR Value 120 SYMBOL res 624 544 R0 SYMATTR InstName R1 SYMATTR Value 2k SYMBOL res 96 144 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R2 SYMATTR Value 10k SYMBOL Comparators\\LT1016 0 528 R0 SYMATTR InstName U1 SYMBOL res 80 240 R0 SYMATTR InstName R3 SYMATTR Value 500k SYMBOL pnp 272 320 R180 WINDOW 0 6 -7 Left 2 WINDOW 3 -1 123 Left 2 SYMATTR InstName Q1 SYMBOL npn 368 432 M0 SYMATTR InstName Q3 SYMBOL res 288 160 R0 SYMATTR InstName R4 SYMATTR Value 2.2k SYMBOL voltage -64 512 R90 WINDOW 0 -32 56 VBottom 2 WINDOW 3 32 56 VTop 2 WINDOW 123 0 0 Left 2 WINDOW 39 0 0 Left 2 SYMATTR InstName V2 SYMATTR Value 10m SYMBOL res -400 640 R0 SYMATTR InstName R5 SYMATTR Value 500 SYMBOL cap 448 160 R0 SYMATTR InstName C1 SYMATTR Value 100p SYMBOL voltage 512 768 R270 WINDOW 0 -32 56 VBottom 2 WINDOW 3 32 56 VTop 2 WINDOW 123 0 0 Left 2 WINDOW 39 0 0 Left 2 SYMATTR InstName V3 SYMATTR Value 5 SYMBOL voltage 128 752 R90 WINDOW 0 -32 56 VBottom 2 WINDOW 3 32 56 VTop 2 WINDOW 123 0 0 Left 2 WINDOW 39 0 0 Left 2 SYMATTR InstName V4 SYMATTR Value 5 SYMBOL res 272 592 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R6 SYMATTR Value 2k SYMBOL res 384 384 R0 SYMATTR InstName R7 SYMATTR Value 10k SYMBOL res 384 496 R0 SYMATTR InstName R8 SYMATTR Value 5k SYMBOL sw -384 448 M180 WINDOW 3 -12 129 Left 2 SYMATTR InstName S1 SYMATTR Value spad SYMBOL voltage -384 432 R0 WINDOW 0 -32 56 VBottom 2 WINDOW 3 32 56 VTop 2 WINDOW 123 0 0 Left 2 WINDOW 39 0 0 Left 2 SYMATTR InstName V5 SYMATTR Value 100 SYMBOL cap -304 416 R0 SYMATTR InstName C2 SYMATTR Value 2p SYMBOL voltage -640 336 R0 WINDOW 0 -61 6 Left 2 WINDOW 3 -245 -38 Left 2 WINDOW 123 0 0 Left 2 WINDOW 39 0 0 Left 2 SYMATTR InstName V6 SYMATTR Value PULSE(0 2 1u 0 0 1n 2u 6) SYMBOL res -64 592 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R9 SYMATTR Value 1k TEXT 728 -32 Left 2 !.tran 10u TEXT 736 56 Left 2 !*LND150 MODEL \n*\n.MODEL LND150 NMOS (LEVEL=3 R S=150.00 NSUB=5.0E13 \n+DELTA=0.1 KAPPA=1.O TP G=1 CGDO=2.1716E-12 \n+RD=40.0 VTO=-1.5 VMAX=1.0E8 ETA=0.1 \n+NFS=6.6E10 TOX=1.0E-7 LD=1 .698E-9 UO=862.425\n+XJ=6.4666E-7 THETA=1.0E-5 CGSO=5.0
9E-10 L=10.0E-6\n+W=600E-6) \n.ENDS\n* TEXT 736 384 Left 2 !.model spad SW(Ron=100 Roff=100Meg Vt=1 Vh=0)