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