* filtered post-dac npn cascode
vsupplyneg vcc 0 dc 30
vsupplypos vee 0 dc -15
* source dac (2 x AD1955)
v1 vref 0 dc 2.6
idac vref vin dc -6.48m ac 1 sin -6.48m 4.32m 1kHz
*rdac vin vref 259.259
* prefilter: 100kHz highpass budget - 2 poles of 155.4k
r1 vin ve 7.5
c1 vin 0 100n
* bias
d1 0 vb 1N4728
r4 vb vcc 1.5k
c3 0 vb 47u
* cascode
r2 vee ve 2.4k
q1 vc vb ve 2N3904
r3 vc vcc 1.33k
c2 vc vcc 1.5n
c4 vc vout 390u
r5 vout 0 1.33k
* General purpose small signal NPN
.MODEL 2N3904 NPN( IS=9.99F NF=1 NR=1 RE=2.51 RC=1 
+      RB=10 VAF=40 VAR=20 ISE=4.03P ISC=4.03P 
+      NE=1.78 NC=1.78 BF=679 
+      BR=5 IKF=13.8M IKR=13.8M CJC=3.6P CJE=3.99P 
+      CJS=0 VJC=878M VJE=16.1 VJS=750M MJC=307M 
+      MJE=2.01 MJS=0 TF=531P TR=69N EG=1.11 
+      KF=0 AF=1 )
* 3.3V 1W zener diode
.MODEL 1N4728 D( IS=15N N=2.22 BV=3.3 IBV=76M 
+      RS=169M CJO=4P VJ=750M M=330M FC=500M 
+      TT=100N EG=1.11 XTI=3 KF=0 AF=1 
+      )
.end
.control
set fourgridsize=1024
set nfreqs=16
set polydegree=3
tran 1u 100m 0 1u
fourier 1k vout
plot vc
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