tacky signal detector

J

John Larkin

Guest
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

--

John Larkin Highland Technology, Inc

lunatic fringe electronics
 
On 17/05/2019 3:45 am, John Larkin wrote:
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
Click to expand...

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
 
On Sat, 18 May 2019 12:22:10 +0100, piglet <erichpwagner@hotmail.com>
wrote:

On 17/05/2019 3:45 am, John Larkin wrote:

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


OK as long the source has a DC return path and no DC offset voltage.
Click to expand...

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

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

Or opamp. Opamps make good comparators for slow signals.

For maximum sleaze get rid of the capacitor and rely on chip input
capacitance!
Click to expand...

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.



--

John Larkin Highland Technology, Inc

lunatic fringe electronics
 
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