Version 4
SHEET 1 880 680
WIRE 208 0 48 0
WIRE 48 48 48 0
WIRE 48 160 48 128
WIRE 192 192 48 192
WIRE 368 192 256 192
WIRE 480 192 368 192
WIRE 48 224 48 192
WIRE 368 224 368 192
WIRE 48 352 48 304
WIRE 368 352 368 304
FLAG 48 160 0
FLAG 208 0 DR1
FLAG 368 352 0
FLAG 48 352 0
FLAG 480 192 out2
SYMBOL voltage 48 32 R0
WINDOW 123 24 124 Left 2
WINDOW 39 0 0 Left 2
SYMATTR InstName V1
SYMATTR Value PULSE(-1 1 0 {1/freq} {1/freq} 0 {2/freq})
SYMBOL res 352 208 R0
SYMATTR InstName R1
SYMATTR Value 4.7k
SYMBOL cap 256 176 R90
WINDOW 0 0 32 VBottom 2
WINDOW 3 32 32 VTop 2
SYMATTR InstName C1
SYMATTR Value 10n
SYMBOL voltage 48 208 R0
WINDOW 3 24 44 Left 2
SYMATTR Value V=135/(1+(10*V(DR1))**2)
SYMATTR InstName B1
SYMATTR Prefix B
TEXT 16 376 Left 2 !.tran 0.05 startup uic
TEXT 48 -56 Left 2 !.param freq=100