* SPICE netlist
D1 Cext1 VCC 1N914
D2 Cext2 VCC 1N914
S1c N003 Cext1 PSW 0 SW
S2c N003 Cext2 NSW 0 SW
M1 N003 VCOin R1 R1 BSS123
M2 N003 Th_ref R2 R2 BSS123
S1v Cext1 VCC NSW 0 SW
S2v Cext2 VCC PSW 0 SW
AsrFf N001 N002 0 0 0 NSW PSW 0 SRFLOP Td=10ns Trise=10ns Tfall=10ns
C1 Cext1 Cext2 10n
A2 Th_ref Cext2 0 0 0 0 N001 0 SCHMITT Vt=0 Vh=.1
A3 Th_ref Cext1 0 0 0 0 N002 0 SCHMITT Vt=0 Vh=.1
V+ VCC 0 {Vdd}
Vctl VCOin 0 PULSE(0 {Vdd} 0 2m 2m 1m)
R1 R1 0 10k
R2 R2 0 100k
Vref Th_ref 0 {Vdd*.6}
Eout VCOout 0 PSW 0 {Vdd}
.tran 5ms
.param Vdd=10

* LTspice schematic (.asc)
Version 4
SHEET 1 1728 352
WIRE -864 0 -864 -64
WIRE -864 144 -864 80
WIRE -720 0 -720 -48
WIRE -720 144 -720 80
WIRE -624 32 -624 0
WIRE -624 144 -624 112
WIRE -512 -64 -528 -64
WIRE -512 32 -512 0
WIRE -512 144 -512 112
WIRE -416 -16 -416 -32
WIRE -416 128 -416 112
WIRE -384 -48 -384 -112
WIRE -384 96 -384 -48
WIRE -352 -112 -384 -112
WIRE -352 -48 -384 -48
WIRE -352 -16 -416 -16
WIRE -352 16 -352 0
WIRE -352 96 -384 96
WIRE -352 128 -416 128
WIRE -352 160 -352 144
WIRE -256 -32 -288 -32
WIRE -256 16 -256 -32
WIRE -256 112 -288 112
WIRE -256 112 -256 64
WIRE -224 16 -256 16
WIRE -224 64 -256 64
WIRE -224 112 -224 96
WIRE -96 16 -128 16
WIRE -96 64 -112 64
WIRE -32 -128 -48 -128
WIRE -32 -64 -32 -80
WIRE 16 -144 16 -176
WIRE 16 -32 16 -64
WIRE 16 0 16 -32
WIRE 64 80 64 64
WIRE 64 144 64 128
WIRE 112 -176 16 -176
WIRE 112 -128 112 -176
WIRE 112 -32 16 -32
WIRE 112 -32 112 -64
WIRE 112 64 112 -32
WIRE 112 176 112 144
WIRE 240 -176 112 -176
WIRE 240 -128 240 -176
WIRE 240 -32 240 -64
WIRE 240 64 240 -32
WIRE 240 176 112 176
WIRE 240 176 240 144
WIRE 288 80 288 64
WIRE 288 144 288 128
WIRE 336 -176 240 -176
WIRE 336 -144 336 -176
WIRE 336 -32 240 -32
WIRE 336 -32 336 -64
WIRE 336 0 336 -32
WIRE 352 -176 336 -176
WIRE 384 -64 384 -80
WIRE 400 -128 384 -128
WIRE 432 64 432 48
WIRE 448 64 432 64
WIRE 496 48 496 0
WIRE 496 176 240 176
WIRE 496 176 496 144
WIRE 544 64 544 48
WIRE 560 64 544 64
WIRE 608 48 608 0
WIRE 608 176 496 176
WIRE 608 176 608 144
WIRE 688 64 688 32
WIRE 688 144 688 112
WIRE 736 144 688 144
WIRE 736 144 736 128
WIRE 736 160 736 144
WIRE 864 48 864 16
WIRE 864 160 864 128
FLAG 16 0 Cext1
IOPIN -400 656 BiDir
FLAG 336 0 Cext2
IOPIN -80 656 BiDir
FLAG 352 -176 VCC
IOPIN -64 480 In
FLAG 288 144 0
FLAG 496 0 R1
IOPIN 80 656 BiDir
FLAG 608 0 R2
IOPIN 192 656 BiDir
FLAG -96 16 PSW
IOPIN -512 672 Out
FLAG -96 64 NSW
IOPIN -512 720 Out
FLAG 64 144 0
FLAG 64 64 PSW
IOPIN -352 720 In
FLAG 288 64 NSW
IOPIN -128 720 In
FLAG -32 -64 0
FLAG 384 -64 0
FLAG 400 -128 PSW
IOPIN -16 528 In
FLAG -48 -128 NSW
IOPIN -464 528 In
FLAG -592 -64 Cext1
FLAG -512 -64 Cext2
FLAG -224 112 0
FLAG -416 -32 Cext2
IOPIN -832 624 In
FLAG -416 112 Cext1
IOPIN -832 768 In
FLAG 864 160 0
FLAG 864 16 Th_ref
IOPIN 448 672 Out
FLAG -352 -112 Th_ref
IOPIN -768 544 In
FLAG -864 144 0
FLAG -864 -64 VCC
IOPIN -1280 592 Out
FLAG -720 144 0
FLAG -720 -48 VCOin
IOPIN -1136 608 Out
FLAG 544 48 Th_ref
IOPIN 128 704 In
FLAG 432 48 VCOin
IOPIN 16 704 In
FLAG -352 16 0
FLAG -352 160 0
FLAG -624 144 0
FLAG -624 0 R1
FLAG -512 144 0
FLAG -512 0 R2
FLAG 736 48 VCOout
IOPIN 320 704 Out
FLAG 736 160 0
FLAG 688 32 PSW
IOPIN 272 688 In
SYMBOL diode 96 -64 M180
SYMATTR InstName D1
SYMATTR Value 1N914
SYMBOL diode 256 -64 R180
SYMATTR InstName D2
SYMATTR Value 1N914
SYMBOL sw 112 160 M180
SYMATTR InstName S1c
SYMBOL sw 240 160 R180
SYMATTR InstName S2c
SYMBOL nmos 448 144 M180
SYMATTR InstName M1
SYMATTR Value BSS123
SYMBOL nmos 560 144 M180
SYMATTR InstName M2
SYMATTR Value BSS123
SYMBOL sw 16 -48 M180
SYMATTR InstName S1v
SYMBOL sw 336 -48 R180
SYMATTR InstName S2v
SYMBOL Digital\\srflop -176 -32 R0
SYMATTR Value Td=10ns Trise=10ns Tfall=10ns
SYMATTR InstName AsrFf
SYMBOL cap -592 -48 R270
SYMATTR InstName C1
SYMATTR Value 10n
SYMBOL Digital\\diffschmtbuf -352 -96 R0
SYMATTR Value Vt=0 Vh=.1
SYMATTR InstName A2
SYMBOL Digital\\diffschmtbuf -352 48 R0
SYMATTR Value Vt=0 Vh=.1
SYMATTR InstName A3
SYMBOL voltage -864 -16 R0
SYMATTR Value {Vdd}
SYMATTR InstName V+
SYMBOL voltage -720 -16 R0
SYMATTR Value PULSE(0 {Vdd} 0 2m 2m 1m)
SYMATTR InstName Vctl
SYMBOL Misc\\EuropeanResistor -640 16 R0
SYMATTR InstName R1
SYMATTR Value 10k
SYMBOL Misc\\EuropeanResistor -528 16 R0
SYMATTR InstName R2
SYMATTR Value 100k
SYMBOL voltage 864 32 R0
SYMATTR InstName Vref
SYMATTR Value {Vdd*.6}
SYMBOL e 736 32 R0
SYMATTR InstName Eout
SYMATTR Value {Vdd}