* 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
A1 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=0.1
A3 Th_ref Cext1 0 0 0 0 N002 0 SCHMITT Vt=0 Vh=0.1
Bref Th_ref 0 V=V(VCC)*0.6
V1 VCC 0 8.0
V2 VCOin 0 3.0
R3 R1 0 10k
R4 R2 0 100k
B1 VCOout 0 V=V(VCC)*V(PSW)
.tran 5ms

* LTspice schematic (.asc)
Version 4
SHEET 1 1296 784
WIRE -632 -200 -632 -264
WIRE -632 -88 -632 -200
WIRE -600 -200 -632 -200
WIRE -600 -168 -648 -168
WIRE -600 -136 -600 -152
WIRE -600 -88 -632 -88
WIRE -600 -56 -648 -56
WIRE -600 -24 -600 -40
WIRE -584 184 -584 152
WIRE -584 296 -584 264
WIRE -504 -184 -536 -184
WIRE -504 -152 -504 -184
WIRE -504 -72 -536 -72
WIRE -504 -72 -504 -104
WIRE -472 -152 -504 -152
WIRE -472 -104 -504 -104
WIRE -472 -56 -472 -72
WIRE -312 -152 -376 -152
WIRE -312 -104 -360 -104
WIRE -280 200 -312 200
WIRE -232 120 -232 72
WIRE -232 264 -232 216
WIRE -200 -296 -200 -312
WIRE -200 -232 -200 -248
WIRE -152 -312 -152 -344
WIRE -152 -200 -152 -232
WIRE -104 -88 -104 -104
WIRE -104 -24 -104 -40
WIRE -56 -344 -152 -344
WIRE -56 -296 -56 -344
WIRE -56 -200 -152 -200
WIRE -56 -200 -56 -232
WIRE -56 -168 -136 -168
WIRE -56 -168 -56 -200
WIRE -56 -104 -56 -168
WIRE -56 8 -56 -24
WIRE -40 200 -72 200
WIRE 8 -344 -56 -344
WIRE 8 -344 8 -392
WIRE 8 8 -56 8
WIRE 8 72 -232 72
WIRE 8 72 8 8
WIRE 8 120 8 72
WIRE 8 264 8 216
WIRE 72 -344 8 -344
WIRE 72 -296 72 -344
WIRE 72 -200 72 -232
WIRE 72 -168 72 -200
WIRE 72 -104 72 -168
WIRE 72 8 8 8
WIRE 72 8 72 -24
WIRE 120 -88 120 -104
WIRE 120 -24 120 -40
WIRE 152 -168 72 -168
WIRE 168 -344 72 -344
WIRE 168 -312 168 -344
WIRE 168 -200 72 -200
WIRE 168 -200 168 -232
WIRE 168 152 168 120
WIRE 168 264 168 232
WIRE 216 -296 216 -312
WIRE 216 -232 216 -248
WIRE 216 120 168 120
WIRE 504 248 504 184
WIRE 504 392 504 328
WIRE 520 -248 520 -280
WIRE 520 -136 520 -168
WIRE 552 -56 520 -56
WIRE 648 -248 648 -280
WIRE 648 -136 648 -168
WIRE 648 -56 616 -56
WIRE 648 248 648 184
WIRE 648 392 648 328
FLAG -136 -168 Cext1
IOPIN -32 224 BiDir
FLAG 152 -168 Cext2
IOPIN 256 224 BiDir
FLAG 8 -392 VCC
IOPIN 112 0 In
FLAG 120 -24 0
FLAG -232 264 R1
IOPIN -128 656 BiDir
FLAG 8 264 R2
IOPIN 112 656 BiDir
FLAG -312 -152 PSW
FLAG -312 -104 NSW
FLAG -104 -24 0
FLAG -104 -104 PSW
FLAG 120 -104 NSW
FLAG -200 -232 0
FLAG 216 -232 0
FLAG 216 -312 PSW
FLAG -200 -312 NSW
FLAG 520 -56 Cext1
FLAG 648 -56 Cext2
FLAG -472 -56 0
FLAG -648 -168 Cext2
FLAG -648 -56 Cext1
FLAG -584 296 0
FLAG -584 152 Th_ref
FLAG -632 -264 Th_ref
FLAG 504 392 0
FLAG 504 184 VCC
FLAG 648 392 0
FLAG 648 184 VCOin
FLAG -72 200 Th_ref
FLAG -312 200 VCOin
IOPIN -208 592 In
FLAG -600 -136 0
FLAG -600 -24 0
FLAG 520 -136 0
FLAG 520 -280 R1
FLAG 648 -136 0
FLAG 648 -280 R2
FLAG 216 120 VCOout
IOPIN 320 512 Out
FLAG 168 264 0
SYMBOL diode -72 -232 M180
SYMATTR InstName D1
SYMATTR Value 1N914
SYMBOL diode 88 -232 R180
SYMATTR InstName D2
SYMATTR Value 1N914
SYMBOL sw -56 -8 M180
SYMATTR InstName S1c
SYMBOL sw 72 -8 R180
SYMATTR InstName S2c
SYMBOL nmos -280 120 R0
SYMATTR InstName M1
SYMATTR Value BSS123
SYMBOL nmos -40 120 R0
SYMATTR InstName M2
SYMATTR Value BSS123
SYMBOL sw -152 -216 M180
SYMATTR InstName S1v
SYMBOL sw 168 -216 R180
SYMATTR InstName S2v
SYMBOL Digital\\srflop -424 -200 R0
SYMATTR InstName A1
SYMATTR Value Td=10ns Trise=10ns Tfall=10ns
SYMBOL cap 552 -40 R270
SYMATTR InstName C1
SYMATTR Value 10n
SYMBOL Digital\\diffschmtbuf -600 -248 R0
SYMATTR InstName A2
SYMATTR Value Vt=0 Vh=0.1
SYMBOL Digital\\diffschmtbuf -600 -136 R0
SYMATTR InstName A3
SYMATTR Value Vt=0 Vh=0.1
SYMBOL bv -584 168 R0
SYMATTR InstName Bref
SYMATTR Value V=V(VCC)*0.6
SYMBOL voltage 504 232 R0
SYMATTR InstName V1
SYMATTR Value 8.0
SYMBOL voltage 648 232 R0
SYMATTR InstName V2
SYMATTR Value 3.0
SYMBOL Misc\\EuropeanResistor 504 -264 R0
SYMATTR InstName R3
SYMATTR Value 10k
SYMBOL Misc\\EuropeanResistor 632 -264 R0
SYMATTR InstName R4
SYMATTR Value 100k
SYMBOL bv 168 136 R0
SYMATTR InstName B1
SYMATTR Value V=V(VCC)*V(PSW)