got a working bjt version of a saw generator (using 3904 and 3906 models). It isn't great but it "works"

diff --git a/xschem/sawgen-bjt.sch b/xschem/sawgen-bjt.sch
new file mode 100644
index 0000000..636cc68
--- /dev/null
+++ b/xschem/sawgen-bjt.sch

@@ -0,0 +1,117 @@
+v {xschem version=2.9.9 file_version=1.2 }
+G {}
+K {}
+V {}
+S {}
+E {}
+N 430 -540 430 -520 { lab=saw}
+N 430 -460 430 -430 { lab=GND}
+N 400 -530 430 -530 { lab=saw}
+N 90 -580 90 -560 { lab=VDD}
+N 90 -500 90 -480 { lab=GND}
+N 300 -700 300 -680 { lab=VDD}
+N 300 -620 300 -590 { lab=vcur}
+N 300 -530 300 -490 { lab=GND}
+N 300 -610 390 -610 { lab=vcur}
+N 430 -580 430 -530 { lab=saw}
+N 430 -540 540 -540 { lab=saw}
+N 540 -540 540 -530 { lab=saw}
+N 540 -470 540 -440 { lab=#net1}
+N 540 -440 590 -440 { lab=#net1}
+N 580 -500 630 -500 { lab=vt}
+N 630 -500 630 -470 { lab=vt}
+N 630 -410 630 -380 { lab=GND}
+N 630 -500 740 -500 { lab=vt}
+N 740 -520 740 -500 { lab=vt}
+N 740 -520 740 -470 { lab=vt}
+N 740 -620 740 -580 { lab=VDD}
+N 740 -410 740 -380 { lab=GND}
+N 430 -760 430 -730 { lab=VDD}
+N 430 -670 430 -640 { lab=#net2}
+C {devices/capa.sym} 430 -490 0 0 {name=C1
+m=1
+value=.1n
+footprint=1206
+device="ceramic capacitor"}
+C {devices/gnd.sym} 430 -430 0 0 {name=l2 lab=GND}
+C {devices/code_shown.sym} -360 -260 0 0 {name=s1 only_toplevel=false value="
+*
+.model 2N3904 NPN(IS=1E-14 VAF=100
++  Bf=300 IKF=0.4 XTB=1.5 BR=4
++  CJC=4E-12  CJE=8E-12 RB=20 RC=0.1 RE=0.1
++  TR=250E-9  TF=350E-12 ITF=1 VTF=2 XTF=3 Vceo=40 Icrating=200m mfg=Philips)
+
+.model 2N3906 PNP(IS=1E-14 VAF=100
++  BF=200 IKF=0.4 XTB=1.5 BR=4
++  CJC=4.5E-12 CJE=10E-12 RB=20 RC=0.1 RE=0.1
++  TR=250E-9   TF=350E-12 ITF=1 VTF=2 XTF=3 Vceo=40  Icrating=200m mfg=Philips)
+
+.OPTION ABSTOL=1e-15.
+.OPTION GMIN=1.0e-12.
+.OPTION ITL1=1e5
+.OPTION RSHUNT=1e12
+.OPTION RELTOL=1e-5
+.OPTION METHOD=gear
+//.lib /usr/share/pdk/sky130A/libs.tech/ngspice/sky130.lib.spice tt
+//.include /usr/share/pdk/sky130A/libs.ref/sky130_fd_sc_hvl/spice/sky130_fd_sc_hvl.spice"}
+C {devices/code_shown.sym} 570 -180 0 0 {name=s2 only_toplevel=false value=".ic V(saw)=0
+.control
+tran 1n 200u
+plot V(saw) V(vcur) V(Vt)
+.endc"}
+C {devices/lab_pin.sym} 400 -530 0 0 {name=l5 sig_type=std_logic lab=saw}
+C {devices/pnp.sym} 410 -610 0 0 {name=Q1
+model=2N3906
+device=2N2907
+footprint=TO92
+area=1
+m=1}
+C {devices/vdd.sym} 430 -760 0 0 {name=l1 lab=VDD}
+C {devices/vdd.sym} 90 -580 0 0 {name=l3 lab=VDD}
+C {devices/gnd.sym} 90 -480 0 0 {name=l4 lab=GND}
+C {devices/vsource.sym} 90 -530 0 0 {name=V1 value=10}
+C {devices/res.sym} 300 -650 0 0 {name=R1
+value=1k
+footprint=1206
+device=resistor
+m=1}
+C {devices/res.sym} 300 -560 0 0 {name=R2
+value=5k
+footprint=1206
+device=resistor
+m=1}
+C {devices/gnd.sym} 300 -490 0 0 {name=l6 lab=GND}
+C {devices/vdd.sym} 300 -700 0 0 {name=l7 lab=VDD}
+C {devices/npn.sym} 610 -440 0 0 {name=Q2
+model=2N3904
+device=MMBT2222
+footprint=SOT23
+area=1
+m=1}
+C {devices/pnp.sym} 560 -500 0 1 {name=Q3
+model=2N3906
+device=2N2907
+footprint=TO92
+area=1
+m=1}
+C {devices/res.sym} 740 -440 0 0 {name=R3
+value=100
+footprint=1206
+device=resistor
+m=1}
+C {devices/res.sym} 740 -550 0 0 {name=R4
+value=100
+footprint=1206
+device=resistor
+m=1}
+C {devices/vdd.sym} 740 -620 0 0 {name=l8 lab=VDD}
+C {devices/gnd.sym} 630 -380 0 0 {name=l9 lab=GND}
+C {devices/gnd.sym} 740 -380 0 0 {name=l10 lab=GND}
+C {devices/lab_pin.sym} 740 -500 0 1 {name=l12 sig_type=std_logic lab=vt
+}
+C {devices/lab_pin.sym} 300 -610 0 0 {name=l13 sig_type=std_logic lab=vcur}
+C {devices/res.sym} 430 -700 0 0 {name=R5
+value=100k
+footprint=1206
+device=resistor
+m=1}

diff --git a/xschem/sawgen-bjt.spice b/xschem/sawgen-bjt.spice
new file mode 100644
index 0000000..85c59fb
--- /dev/null
+++ b/xschem/sawgen-bjt.spice

@@ -0,0 +1,43 @@
+**.subckt sawgen-bjt
+C1 saw GND .1n m=1
+Q1 saw vcur net2 2N3906 area=1 m=1
+V1 VDD GND 10
+R1 VDD vcur 1k m=1
+R2 vcur GND 5k m=1
+Q2 vt net1 GND 2N3904 area=1 m=1
+Q3 net1 vt saw 2N3906 area=1 m=1
+R3 vt GND 100 m=1
+R4 VDD vt 100 m=1
+R5 VDD net2 100k m=1
+**** begin user architecture code
+
+
+*
+.model 2N3904 NPN(IS=1E-14 VAF=100   Bf=300 IKF=0.4 XTB=1.5 BR=4   CJC=4E-12  CJE=8E-12 RB=20 RC=0.1
++ RE=0.1   TR=250E-9  TF=350E-12 ITF=1 VTF=2 XTF=3 Vceo=40 Icrating=200m mfg=Philips)
+
+.model 2N3906 PNP(IS=1E-14 VAF=100   BF=200 IKF=0.4 XTB=1.5 BR=4   CJC=4.5E-12 CJE=10E-12 RB=20
++ RC=0.1 RE=0.1   TR=250E-9   TF=350E-12 ITF=1 VTF=2 XTF=3 Vceo=40  Icrating=200m mfg=Philips)
+
+.OPTION ABSTOL=1e-15.
+.OPTION GMIN=1.0e-12.
+.OPTION ITL1=1e5
+.OPTION RSHUNT=1e12
+.OPTION RELTOL=1e-5
+.OPTION METHOD=gear
+//.lib /usr/share/pdk/sky130A/libs.tech/ngspice/sky130.lib.spice tt
+//.include /usr/share/pdk/sky130A/libs.ref/sky130_fd_sc_hvl/spice/sky130_fd_sc_hvl.spice
+
+
+.ic V(saw)=0
+.control
+tran 1n 200u
+plot V(saw) V(vcur) V(Vt)
+.endc
+
+**** end user architecture code
+**.ends
+.GLOBAL GND
+.GLOBAL VDD
+** flattened .save nodes
+.end