tacky signal detector

We'd like to light up an LED when the customer gives us an input, nominally 1 volt peak at 10 MHz, but could be less.

This detector might work. It depends on schottky diode leakage to discharge the cap. It will drive an opamp, or a comparator, with pA bias current. We'd threshold that at 20 mV or some such to turn on the LED.

Version 4 SHEET 1 880 680 WIRE -304 96 -576 96 WIRE -96 128 -160 128 WIRE 0 128 -96 128 WIRE 144 128 64 128 WIRE 208 128 144 128 WIRE -304 160 -464 160 WIRE 208 160 208 128 WIRE -576 176 -576 96 WIRE -464 176 -464 160 WIRE 208 288 208 224 WIRE -576 320 -576 256 WIRE -464 320 -464 256 FLAG 208 288 0 FLAG -96 128 SIG FLAG 144 128 OUT FLAG -576 320 0 FLAG -464 320 0 SYMBOL diode 0 144 R270 WINDOW 0 78 34 VTop 2 WINDOW 3 70 35 VBottom 2 SYMATTR InstName D2 SYMATTR Value Ds SYMBOL cap 192 160 R0 WINDOW 0 68 25 Left 2 WINDOW 3 55 54 Left 2 SYMATTR InstName C1 SYMATTR Value 200p SYMBOL SpecialFunctions\\modulate -304 96 R0 WINDOW 0 56 33 Left 2 WINDOW 3 -60 -63 Left 2 SYMATTR InstName A1 SYMATTR Value mark=10Meg space=0 SYMBOL voltage -576 160 R0 WINDOW 0 26 105 Left 2 WINDOW 3 34 135 Left 2 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR InstName V2 SYMATTR Value 1 SYMBOL voltage -464 160 R0 WINDOW 0 55 79 Left 2 WINDOW 3 23 118 Left 2 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR InstName V1 SYMATTR Value PULSE(0 1 500u 4m 0 500um) TEXT -416 352 Left 2 !.MODEL Ds D(IS=130n RS=4.5 N=1.08 XTI=1.8 EG=.68\n+ CJO=260f M=.047 VJ=.11 FC=.5 BV=4 IBV=10U TT=25p) TEXT -16 312 Left 2 !.tran 8m TEXT -64 272 Left 2 ;JL May 16, 2019 TEXT -96 232 Left 2 ;Tacky Signal Detector TEXT -8 168 Left 2 ;SMS7621

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John Larkin         Highland Technology, Inc 

lunatic fringe electronics
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John Larkin
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OK as long the source has a DC return path and no DC offset voltage.

Simplicity is disguised by the 20-50 transistors doing all the legwork inside the comparator chip :)

For maximum sleaze get rid of the capacitor and rely on chip input capacitance!

piglet

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piglet

It's a MiniCircuits RF transformer. DC offset is small.

Or opamp. Opamps make good comparators for slow signals.

I was thinking of having the diode drive the summing point of the opamp, to keep zero volts across the diode at all times. Gotta try that. The trick there is to not load the source much at high signal level.

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John Larkin         Highland Technology, Inc 

lunatic fringe electronics
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John Larkin

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