C
colin
Hi, Im adding a bias generator to improve the sensitivity/linearity of a
simple schotky diode multiplier RF vpp sniffer probe, using 2 aaaa battery
so it
can last a few years with no off switch. its only a bias generator rather
than an amplifier so it can still measure input voltages of say 5vpp or more
with only 2 batteries, (idealy it would just use 1)
using a micropower op amp I can easily supply a bias voltage tracked to the
current through the detector, wich makes it quite linear down to well below
100mv, however the sensitivity falls off progresivly below 40 mv, presumably
becuase the detector diodes arn't so nonlinear for very low voltage swings.
I have a spare op amp I could use to try and do slope compensation but is
there an easier way to compensate for this ?
Ive looked at several circuits and ICs on the web and they go down to about
100mv but are more than just a simple bias generator and so wont work with
just 2 batteries, and there are of course profesional units wich go down
to at least 10mv but can hardly be put inside a pen size case.
It might not be worthwhile trying to make it sensitve below 40mv anyway but
the challange is there !
Colin =^.^=
swcad file of current design ... (just for simulation uses lt1462 with +/-
3v instead of target ts942) :-
Version 4
SHEET 1 1448 1056
WIRE -224 832 -224 816
WIRE -224 864 -224 832
WIRE -224 992 -224 944
WIRE -160 816 -224 816
WIRE 80 416 80 368
WIRE 80 592 80 560
WIRE 80 704 80 656
WIRE 80 720 80 704
WIRE 80 816 -96 816
WIRE 80 816 80 784
WIRE 80 864 80 816
WIRE 80 992 -224 992
WIRE 80 992 80 928
WIRE 224 368 80 368
WIRE 224 560 224 368
WIRE 224 704 80 704
WIRE 224 704 224 624
WIRE 224 752 224 704
WIRE 224 992 80 992
WIRE 224 992 224 816
WIRE 400 704 224 704
WIRE 400 704 400 672
WIRE 400 816 400 704
WIRE 480 784 480 672
WIRE 480 800 480 784
WIRE 480 992 224 992
WIRE 480 992 480 880
WIRE 496 368 224 368
WIRE 496 704 496 368
WIRE 528 784 480 784
WIRE 576 672 480 672
WIRE 576 704 496 704
WIRE 864 368 496 368
WIRE 864 480 864 368
WIRE 864 688 640 688
WIRE 864 688 864 560
WIRE 864 784 608 784
WIRE 864 784 864 688
WIRE 864 992 480 992
WIRE 912 368 864 368
WIRE 976 368 912 368
WIRE 976 720 976 368
WIRE 976 992 864 992
WIRE 976 992 976 800
WIRE 1168 704 1168 672
FLAG -224 832 sigin
FLAG 400 592 v1.5
FLAG 608 656 v1.5
FLAG 912 368 vdmm+
FLAG 400 896 v-1.5
FLAG 608 720 v-1.5
FLAG -464 832 vin
FLAG 400 704 0
FLAG -464 912 0
FLAG 864 992 vdmm-
FLAG 1168 784 0
FLAG 1168 672 vout
SYMBOL schottky 96 784 R180
WINDOW 0 24 72 Left 0
WINDOW 3 24 0 Left 0
SYMATTR InstName D2
SYMATTR Value hsms2820
SYMATTR Description Diode
SYMATTR Type diode
SYMBOL cap 208 560 R0
SYMATTR InstName C1
SYMATTR Value 50p
SYMBOL voltage 400 576 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V1
SYMATTR Value 3
SYMBOL schottky 64 496 R0
SYMATTR InstName D4
SYMATTR Value hsms2820
SYMATTR Description Diode
SYMATTR Type diode
SYMBOL schottky 96 928 R180
WINDOW 0 24 72 Left 0
WINDOW 3 24 0 Left 0
SYMATTR InstName D5
SYMATTR Value hsms2820
SYMATTR Description Diode
SYMATTR Type diode
SYMBOL cap -96 800 R90
WINDOW 0 0 32 VBottom 0
WINDOW 3 32 32 VTop 0
SYMATTR InstName C2
SYMATTR Value 100p
SYMBOL cap 208 752 R0
SYMATTR InstName C3
SYMATTR Value 50p
SYMBOL schottky 64 592 R0
SYMATTR InstName D1
SYMATTR Value hsms2820
SYMATTR Description Diode
SYMATTR Type diode
SYMBOL res 464 784 R0
SYMATTR InstName R2
SYMATTR Value 50e6
SYMBOL res 848 464 R0
SYMATTR InstName R4
SYMATTR Value 1.3e6
SYMBOL res 624 768 R90
WINDOW 0 0 56 VBottom 0
WINDOW 3 32 56 VTop 0
SYMATTR InstName R1
SYMATTR Value 50e6
SYMBOL voltage 400 800 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V2
SYMATTR Value 3
SYMBOL bv -224 848 R0
SYMATTR InstName B1
SYMATTR Value V=sin(time*2*pi*F1)*v(Vin)/2
SYMBOL res 960 704 R0
SYMATTR InstName R3
SYMATTR Value 10e6
SYMBOL bv -464 816 R0
SYMATTR InstName B2
SYMATTR Value V=V1*time/tend
SYMBOL res 64 400 R0
SYMATTR InstName R6
SYMATTR Value 120k
SYMBOL bv 1168 688 R0
SYMATTR InstName B3
SYMATTR Value V=v(vdmm+,vdmm-)
SYMBOL Opamps\\LT1462 608 624 R0
SYMATTR InstName U1
TEXT -370 1040 Left 0 !.tran 100ms
TEXT 592 848 Left 0 !.parameter F1 1e5\n.parameter V1 1\n.parameter tend .1
simple schotky diode multiplier RF vpp sniffer probe, using 2 aaaa battery
so it
can last a few years with no off switch. its only a bias generator rather
than an amplifier so it can still measure input voltages of say 5vpp or more
with only 2 batteries, (idealy it would just use 1)
using a micropower op amp I can easily supply a bias voltage tracked to the
current through the detector, wich makes it quite linear down to well below
100mv, however the sensitivity falls off progresivly below 40 mv, presumably
becuase the detector diodes arn't so nonlinear for very low voltage swings.
I have a spare op amp I could use to try and do slope compensation but is
there an easier way to compensate for this ?
Ive looked at several circuits and ICs on the web and they go down to about
100mv but are more than just a simple bias generator and so wont work with
just 2 batteries, and there are of course profesional units wich go down
to at least 10mv but can hardly be put inside a pen size case.
It might not be worthwhile trying to make it sensitve below 40mv anyway but
the challange is there !
Colin =^.^=
swcad file of current design ... (just for simulation uses lt1462 with +/-
3v instead of target ts942) :-
Version 4
SHEET 1 1448 1056
WIRE -224 832 -224 816
WIRE -224 864 -224 832
WIRE -224 992 -224 944
WIRE -160 816 -224 816
WIRE 80 416 80 368
WIRE 80 592 80 560
WIRE 80 704 80 656
WIRE 80 720 80 704
WIRE 80 816 -96 816
WIRE 80 816 80 784
WIRE 80 864 80 816
WIRE 80 992 -224 992
WIRE 80 992 80 928
WIRE 224 368 80 368
WIRE 224 560 224 368
WIRE 224 704 80 704
WIRE 224 704 224 624
WIRE 224 752 224 704
WIRE 224 992 80 992
WIRE 224 992 224 816
WIRE 400 704 224 704
WIRE 400 704 400 672
WIRE 400 816 400 704
WIRE 480 784 480 672
WIRE 480 800 480 784
WIRE 480 992 224 992
WIRE 480 992 480 880
WIRE 496 368 224 368
WIRE 496 704 496 368
WIRE 528 784 480 784
WIRE 576 672 480 672
WIRE 576 704 496 704
WIRE 864 368 496 368
WIRE 864 480 864 368
WIRE 864 688 640 688
WIRE 864 688 864 560
WIRE 864 784 608 784
WIRE 864 784 864 688
WIRE 864 992 480 992
WIRE 912 368 864 368
WIRE 976 368 912 368
WIRE 976 720 976 368
WIRE 976 992 864 992
WIRE 976 992 976 800
WIRE 1168 704 1168 672
FLAG -224 832 sigin
FLAG 400 592 v1.5
FLAG 608 656 v1.5
FLAG 912 368 vdmm+
FLAG 400 896 v-1.5
FLAG 608 720 v-1.5
FLAG -464 832 vin
FLAG 400 704 0
FLAG -464 912 0
FLAG 864 992 vdmm-
FLAG 1168 784 0
FLAG 1168 672 vout
SYMBOL schottky 96 784 R180
WINDOW 0 24 72 Left 0
WINDOW 3 24 0 Left 0
SYMATTR InstName D2
SYMATTR Value hsms2820
SYMATTR Description Diode
SYMATTR Type diode
SYMBOL cap 208 560 R0
SYMATTR InstName C1
SYMATTR Value 50p
SYMBOL voltage 400 576 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V1
SYMATTR Value 3
SYMBOL schottky 64 496 R0
SYMATTR InstName D4
SYMATTR Value hsms2820
SYMATTR Description Diode
SYMATTR Type diode
SYMBOL schottky 96 928 R180
WINDOW 0 24 72 Left 0
WINDOW 3 24 0 Left 0
SYMATTR InstName D5
SYMATTR Value hsms2820
SYMATTR Description Diode
SYMATTR Type diode
SYMBOL cap -96 800 R90
WINDOW 0 0 32 VBottom 0
WINDOW 3 32 32 VTop 0
SYMATTR InstName C2
SYMATTR Value 100p
SYMBOL cap 208 752 R0
SYMATTR InstName C3
SYMATTR Value 50p
SYMBOL schottky 64 592 R0
SYMATTR InstName D1
SYMATTR Value hsms2820
SYMATTR Description Diode
SYMATTR Type diode
SYMBOL res 464 784 R0
SYMATTR InstName R2
SYMATTR Value 50e6
SYMBOL res 848 464 R0
SYMATTR InstName R4
SYMATTR Value 1.3e6
SYMBOL res 624 768 R90
WINDOW 0 0 56 VBottom 0
WINDOW 3 32 56 VTop 0
SYMATTR InstName R1
SYMATTR Value 50e6
SYMBOL voltage 400 800 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V2
SYMATTR Value 3
SYMBOL bv -224 848 R0
SYMATTR InstName B1
SYMATTR Value V=sin(time*2*pi*F1)*v(Vin)/2
SYMBOL res 960 704 R0
SYMATTR InstName R3
SYMATTR Value 10e6
SYMBOL bv -464 816 R0
SYMATTR InstName B2
SYMATTR Value V=V1*time/tend
SYMBOL res 64 400 R0
SYMATTR InstName R6
SYMATTR Value 120k
SYMBOL bv 1168 688 R0
SYMATTR InstName B3
SYMATTR Value V=v(vdmm+,vdmm-)
SYMBOL Opamps\\LT1462 608 624 R0
SYMATTR InstName U1
TEXT -370 1040 Left 0 !.tran 100ms
TEXT 592 848 Left 0 !.parameter F1 1e5\n.parameter V1 1\n.parameter tend .1
