* SPICE netlist
S7 N003 00 V_0_deg 0 MYSW
S2 N003 01 V_90_deg 0 MYSW
S4 N003 11 V_180_deg 0 MYSW
S6 N003 10 V_270_deg 0 MYSW
V3 N003 0 SINE(2.5 1u {RF_Freq}) AC 1 Rser=50
V4 +5V 0 5
V5 0 -5V 5
V1 V_0_deg 0 PULSE(0 1 0 0.001p 0.001p {SW_time} {4*SW_time})
V2 V_90_deg 0 PULSE(0 1 {SW_time} 0.001p 0.001p {SW_time} {4*SW_time})
V6 V_180_deg 0 PULSE(0 1 {2*SW_time} 0.001p 0.001p {SW_time} {4*SW_time})
V7 V_270_deg 0 PULSE(0 1 {3*SW_time} 0.001p 0.001p {SW_time} {4*SW_time})
C1 0 N007 {C_Sample}
C7 0 N009 {C_Sample}
R24 N007 01 0.1
R25 N009 10 0.1
C3 0 N002 {C_Sample}
C13 0 N005 {C_Sample}
R5 N002 00 1
R7 N005 11 1
R1 V_I N006 100k
R2 N006 N007 10
R3 N008 N009 10
R4 V_Q N001 100k
R6 N001 N002 10
R8 N004 N005 10
C2 V_I N006 150pF
XU1 N004 N001 +5V 0 V_Q level1 Avol=1Meg GBW=10Meg Vos=0 En=0 Enk=0 In=0 Ink=0 Rin=500Meg ;pnba In+)In-)V+)V-)OUT
XU2 N008 N006 +5V 0 V_I level1 Avol=1Meg GBW=10Meg Vos=0 En=0 Enk=0 In=0 Ink=0 Rin=500Meg ;pnba In+)In-)V+)V-)OUT
C4 V_Q N001 150pF
.tran 0 .7m .2m
;.ac dec 10 10 1000Meg;
;.noise V(V_outQ) V3 dec 10 10 100meg
;.op
.param RF_freq=15Meg LO_freq={RF_freq - Audio_freq} LO_period={1/LO_freq} SW_time={LO_period/4}
.param C_Sample=4.7n
;step dec param Audio_freq 1000 10000000 1
.param Audio_freq=10000

* LTspice schematic (.asc)
Version 4
SHEET 1 2224 1328
WIRE 680 -648 536 -648
WIRE 824 -648 744 -648
WIRE 536 -568 536 -648
WIRE 632 -568 536 -568
WIRE 824 -568 824 -648
WIRE 824 -568 712 -568
WIRE -168 -504 -216 -504
WIRE 24 -504 -88 -504
WIRE 120 -504 24 -504
WIRE -648 -488 -728 -488
WIRE -360 -488 -568 -488
WIRE 24 -472 24 -504
WIRE -472 -440 -584 -440
WIRE 120 -440 120 -504
WIRE 424 -440 120 -440
WIRE 536 -440 536 -568
WIRE 536 -440 504 -440
WIRE 600 -440 536 -440
WIRE 600 -424 600 -440
WIRE 632 -424 600 -424
WIRE 824 -408 824 -568
WIRE 824 -408 696 -408
WIRE 888 -408 824 -408
WIRE 24 -392 24 -408
WIRE 632 -392 600 -392
WIRE -728 -376 -728 -488
WIRE -648 -376 -728 -376
WIRE -360 -376 -568 -376
WIRE 424 -376 120 -376
WIRE 600 -376 600 -392
WIRE 600 -376 504 -376
WIRE -472 -328 -584 -328
WIRE 904 -328 760 -328
WIRE 1048 -328 968 -328
WIRE -1000 -312 -1080 -312
WIRE -728 -312 -728 -376
WIRE -728 -312 -920 -312
WIRE -168 -312 -216 -312
WIRE 24 -312 -88 -312
WIRE 120 -312 120 -376
WIRE 120 -312 24 -312
WIRE -1080 -296 -1080 -312
WIRE 24 -280 24 -312
WIRE -728 -264 -728 -312
WIRE -648 -264 -728 -264
WIRE -360 -264 -568 -264
WIRE 760 -248 760 -328
WIRE 856 -248 760 -248
WIRE 1048 -248 1048 -328
WIRE 1048 -248 936 -248
WIRE -472 -216 -584 -216
WIRE 24 -200 24 -216
WIRE 312 -184 168 -184
WIRE 504 -184 392 -184
WIRE 600 -184 504 -184
WIRE -728 -152 -728 -264
WIRE -648 -152 -728 -152
WIRE -360 -152 -568 -152
WIRE 504 -152 504 -184
WIRE 600 -120 600 -184
WIRE 648 -120 600 -120
WIRE 760 -120 760 -248
WIRE 760 -120 728 -120
WIRE 824 -120 760 -120
WIRE -472 -104 -584 -104
WIRE 824 -104 824 -120
WIRE 856 -104 824 -104
WIRE 1048 -88 1048 -248
WIRE 1048 -88 920 -88
WIRE 1112 -88 1048 -88
WIRE 504 -72 504 -88
WIRE 856 -72 824 -72
WIRE 648 -56 600 -56
WIRE 824 -56 824 -72
WIRE 824 -56 728 -56
WIRE 312 8 168 8
WIRE 504 8 392 8
WIRE 600 8 600 -56
WIRE 600 8 504 8
WIRE 504 40 504 8
WIRE 504 120 504 104
WIRE -1000 360 -1112 360
WIRE -184 360 -296 360
WIRE -1112 392 -1112 360
WIRE -296 392 -296 360
WIRE 904 456 904 440
WIRE 904 456 824 456
WIRE 904 472 904 456
WIRE 824 488 824 456
WIRE -1000 552 -1112 552
WIRE -184 552 -296 552
WIRE -1112 584 -1112 552
WIRE -296 584 -296 552
FLAG -632 -440 0
FLAG -632 -328 0
FLAG -632 -216 0
FLAG -632 -104 0
FLAG -1080 -296 0
FLAG 904 360 +5V
FLAG 824 488 0
FLAG 904 552 -5V
FLAG -472 -440 V_0_deg
FLAG -472 -328 V_90_deg
FLAG -472 -216 V_180_deg
FLAG -472 -104 V_270_deg
FLAG -1112 472 0
FLAG -1000 360 V_0_deg
FLAG -1112 664 0
FLAG -1000 552 V_90_deg
FLAG -296 472 0
FLAG -184 360 V_180_deg
FLAG -296 664 0
FLAG -184 552 V_270_deg
FLAG -360 -488 00
FLAG -360 -264 11
FLAG 504 120 0
FLAG 504 -72 0
FLAG -360 -376 01
FLAG -360 -152 10
FLAG 24 -200 0
FLAG 24 -392 0
FLAG -216 -312 11
FLAG -216 -504 00
FLAG 168 8 10
FLAG 168 -184 01
FLAG 888 -120 +5V
FLAG 664 -440 +5V
FLAG 1112 -88 V_I
FLAG 888 -408 V_Q
FLAG 664 -376 0
FLAG 888 -56 0
SYMBOL sw -664 -488 R270
SYMATTR InstName S7
SYMATTR Value MYSW
SYMBOL sw -664 -376 R270
SYMATTR InstName S2
SYMATTR Value MYSW
SYMBOL sw -664 -264 R270
SYMATTR InstName S4
SYMATTR Value MYSW
SYMBOL sw -664 -152 R270
SYMATTR InstName S6
SYMATTR Value MYSW
SYMBOL voltage -904 -312 R90
SYMATTR InstName V3
SYMATTR Value SINE(2.5 1u {RF_Freq})
SYMATTR Value2 AC 1
SYMATTR SpiceLine Rser=50
SYMBOL voltage 904 344 R0
SYMATTR InstName V4
SYMATTR Value 5
SYMBOL voltage 904 456 R0
SYMATTR InstName V5
SYMATTR Value 5
SYMBOL voltage -1112 376 R0
SYMATTR InstName V1
SYMATTR Value PULSE(0 1 0 0.001p 0.001p {SW_time} {4*SW_time})
SYMBOL voltage -1112 568 R0
SYMATTR InstName V2
SYMATTR Value PULSE(0 1 {SW_time} 0.001p 0.001p {SW_time} {4*SW_time})
SYMBOL voltage -296 376 R0
SYMATTR InstName V6
SYMATTR Value PULSE(0 1 {2*SW_time} 0.001p 0.001p {SW_time} {4*SW_time})
SYMBOL voltage -296 568 R0
SYMATTR InstName V7
SYMATTR Value PULSE(0 1 {3*SW_time} 0.001p 0.001p {SW_time} {4*SW_time})
SYMBOL cap 520 -88 R180
SYMATTR InstName C1
SYMATTR Value {C_Sample}
SYMBOL cap 520 104 R180
SYMATTR InstName C7
SYMATTR Value {C_Sample}
SYMBOL res 408 -200 R90
SYMATTR InstName R24
SYMATTR Value 0.1
SYMBOL res 408 -8 R90
SYMATTR InstName R25
SYMATTR Value 0.1
SYMBOL cap 40 -408 R180
SYMATTR InstName C3
SYMATTR Value {C_Sample}
SYMBOL cap 40 -216 R180
SYMATTR InstName C13
SYMATTR Value {C_Sample}
SYMBOL res -72 -520 R90
SYMATTR InstName R5
SYMATTR Value 1
SYMBOL res -72 -328 R90
SYMATTR InstName R7
SYMATTR Value 1
SYMBOL res 952 -264 R90
SYMATTR InstName R1
SYMATTR Value 100k
SYMBOL res 744 -136 R90
SYMATTR InstName R2
SYMATTR Value 10
SYMBOL res 744 -72 R90
SYMATTR InstName R3
SYMATTR Value 10
SYMBOL res 728 -584 R90
SYMATTR InstName R4
SYMATTR Value 100k
SYMBOL res 520 -456 R90
SYMATTR InstName R6
SYMATTR Value 10
SYMBOL res 520 -392 R90
SYMATTR InstName R8
SYMATTR Value 10
SYMBOL cap 968 -344 R90
SYMATTR InstName C2
SYMATTR Value 150pF
SYMBOL OpAmps\\UniversalOpAmp 664 -408 R0
SYMATTR InstName U1
SYMBOL OpAmps\\UniversalOpAmp 888 -88 R0
SYMATTR InstName U2
SYMBOL cap 744 -664 R90
SYMATTR InstName C4
SYMATTR Value 150pF