* filtered post dac pnp cascode
* Spice version:  Spice Opus 2.31
vsupplyneg vcc 0 dc -30
vsupplypos vee 0 dc 15
* source dac with output characteristics of pcm1794
idac 0 vin dc 6.2m ac 1 sin 6.2m 3.9m 1kHz
rdac vin 0 470
* prefilter: 100kHz highpass budget - 2 poles of 155.4k
r1 vin ve 8.2
c1 vin 0 100n
* bias
d1 0 vb 1N914
r4 vb vcc 1.8k
c3 0 vb 47u
* cascode
r2 vee ve 1.6k
q1 vc vb ve 2N3906
r3 vc vcc 1.43k
c2 vc vcc 1.3n
c4 vc vout 330u
r5 vout 0 1.43k
.MODEL 2N3906 PNP( IS=1.77F RE=732M RC=1 RB=10 VAF=23.3 
+      VAR=11.7 ISE=73.2F ISC=73.2F NE=1.62 NC=1.62 
+      BF=289 BR=5 IKF=29.2M IKR=29.2M CJC=6.95P 
+      CJE=6.86P VJC=374M VJE=100M MJC=340M MJE=199M 
+      TF=637P TR=82.8N )
.MODEL 1N914 d (
+IS=6.47335e-11 RS=1.14528 N=1.32752 EG=1.02272
+XTI=4 BV=110 IBV=5e-06 CJO=2.99131e-12
+VJ=1.31352 M=0.9 FC=0.5 TT=2.59685e-09
+KF=0 AF=1 )
.end
.control
set fourgridsize=1024
set nfreqs=16
set polydegree=3
tran 1u 100m 0 1u
fourier 1k vout
noise v(vout) idac dec 10 20Hz 20kHz
print db(onoise_total)/-2
set units=degrees
ac dec 10 10 1meg
plot db(vout/vout[0])
.endc