added VCO
diff --git a/docs/VCO_10p_external_cap.png b/docs/VCO_10p_external_cap.png
new file mode 100644
index 0000000..40de42d
--- /dev/null
+++ b/docs/VCO_10p_external_cap.png
Binary files differ
diff --git a/docs/VCO_no_external_cap.png b/docs/VCO_no_external_cap.png
new file mode 100644
index 0000000..c96d533
--- /dev/null
+++ b/docs/VCO_no_external_cap.png
Binary files differ
diff --git a/mag/VCO_Ring_OSC_v4.mag b/mag/VCO_Ring_OSC_v4.mag
new file mode 100644
index 0000000..f6c6d7b
--- /dev/null
+++ b/mag/VCO_Ring_OSC_v4.mag
@@ -0,0 +1,63 @@
+magic
+tech sky130A
+timestamp 1623667149
+<< mvpsubdiff >>
+rect 875 0 1075 25
+<< locali >>
+rect 875 0 1075 25
+<< metal1 >>
+rect 875 456 885 554
+rect 1065 456 1075 554
+rect -10 62 8 429
+rect 875 176 1075 215
+rect 1391 62 1435 429
+rect 875 0 1075 25
+<< via1 >>
+rect 157 182 192 209
+rect 332 182 367 209
+<< metal2 >>
+rect 151 209 198 215
+rect 151 182 157 209
+rect 192 182 198 209
+rect 151 -12 198 182
+rect 326 209 373 215
+rect 326 182 332 209
+rect 367 182 373 209
+rect 326 -12 373 182
+use inverter3v3 inverter3v3_6
+timestamp 1623667149
+transform 1 0 1250 0 1 0
+box 0 0 175 554
+use inverter3v3 inverter3v3_5
+timestamp 1623667149
+transform 1 0 1075 0 1 0
+box 0 0 175 554
+use inverter3v3 inverter3v3_4
+timestamp 1623667149
+transform 1 0 700 0 1 0
+box 0 0 175 554
+use inverter3v3 inverter3v3_0
+timestamp 1623667149
+transform 1 0 0 0 1 0
+box 0 0 175 554
+use inverter3v3 inverter3v3_1
+timestamp 1623667149
+transform 1 0 175 0 1 0
+box 0 0 175 554
+use inverter3v3 inverter3v3_2
+timestamp 1623667149
+transform 1 0 350 0 1 0
+box 0 0 175 554
+use inverter3v3 inverter3v3_3
+timestamp 1623667149
+transform 1 0 525 0 1 0
+box 0 0 175 554
+<< labels >>
+rlabel metal1 1433 187 1433 187 7 OUT
+rlabel metal1 969 8 969 8 1 GND
+rlabel metal1 1069 492 1069 492 1 VCC
+rlabel metal1 881 487 881 487 1 VADJ
+rlabel metal2 178 -7 178 -7 1 OUT1
+rlabel metal2 348 -5 348 -5 1 OUT2
+rlabel metal1 -7 186 -7 186 3 IN
+<< end >>
diff --git a/mag/inverter3v3.ext b/mag/inverter3v3.ext
new file mode 100644
index 0000000..7f388d7
--- /dev/null
+++ b/mag/inverter3v3.ext
@@ -0,0 +1,21 @@
+timestamp 1623667149
+version 8.3
+tech sky130A
+style ngspice()
+scale 1000 1 1e+06
+resistclasses 2200000 3050000 1700000 3050000 120000 197000 114000 191000 120000 197000 114000 191000 48200 319800 2000000 48200 48200 12200 125 125 47 47 29 5
+parameters sky130_fd_pr__nfet_g5v0d10v5 l=l w=w a1=as p1=ps a2=ad p2=pd
+parameters sky130_fd_pr__nfet_20v0 l=l w=w a1=as a2=ad p1=ps p2=pd
+parameters sky130_fd_pr__pfet_g5v0d10v5 l=l w=w a1=as p1=ps a2=ad p2=pd
+parameters sky130_fd_pr__pfet_20v0 l=l w=w a1=as a2=ad p1=ps p2=pd
+node "OUT" 1866 662.529 112 62 mvndif 0 0 0 0 0 0 0 0 0 0 0 0 2900 258 5800 458 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 8700 716 11969 860 0 0 0 0 0 0 0 0 0 0
+node "IN" 392 523.605 62 49 p 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 19650 886 0 0 1188 138 3822 274 0 0 0 0 0 0 0 0 0 0
+node "VDD" 5100 1550.43 0 196 nw 0 0 0 0 62650 1066 0 0 0 0 0 0 6804 342 5800 458 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 22950 1004 23733 1000 0 0 0 0 0 0 0 0 0 0
+substrate "GND" 0 0 0 0 mvppd 0 0 0 0 0 0 0 0 0 0 0 0 2900 258 4375 400 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 7275 658 8348 674 0 0 0 0 0 0 0 0 0 0
+cap "OUT" "IN" 465.237
+cap "OUT" "VDD" 399.946
+cap "VDD" "IN" 302.597
+device msubckt sky130_fd_pr__nfet_g5v0d10v5 62 62 63 63 l=50 w=100 "GND" "IN" 100 0 "GND" 100 0 "OUT" 100 0
+device msubckt sky130_fd_pr__pfet_g5v0d10v5 62 229 63 230 l=50 w=200 "VDD" "IN" 100 0 "VDD" 200 0 "OUT" 200 0
+subcap "OUT" -235.988
+subcap "IN" -235.787
diff --git a/mag/inverter3v3.mag b/mag/inverter3v3.mag
new file mode 100644
index 0000000..7115585
--- /dev/null
+++ b/mag/inverter3v3.mag
@@ -0,0 +1,127 @@
+magic
+tech sky130A
+timestamp 1623667149
+<< nwell >>
+rect 0 196 175 554
+<< mvnmos >>
+rect 62 62 112 162
+<< mvpmos >>
+rect 62 229 112 429
+<< mvndiff >>
+rect 33 150 62 162
+rect 33 74 38 150
+rect 56 74 62 150
+rect 33 62 62 74
+rect 112 150 141 162
+rect 112 74 119 150
+rect 137 74 141 150
+rect 112 62 141 74
+<< mvpdiff >>
+rect 33 416 62 429
+rect 33 240 38 416
+rect 56 240 62 416
+rect 33 229 62 240
+rect 112 416 141 429
+rect 112 240 119 416
+rect 137 240 141 416
+rect 112 229 141 240
+<< mvndiffc >>
+rect 38 74 56 150
+rect 119 74 137 150
+<< mvpdiffc >>
+rect 38 240 56 416
+rect 119 240 137 416
+<< mvpsubdiff >>
+rect 0 22 175 25
+rect 0 3 15 22
+rect 160 3 175 22
+rect 0 0 175 3
+<< mvnsubdiff >>
+rect 33 507 141 519
+rect 33 456 141 468
+<< mvpsubdiffcont >>
+rect 15 3 160 22
+<< mvnsubdiffcont >>
+rect 33 468 141 507
+<< poly >>
+rect 62 429 112 442
+rect 62 204 112 229
+rect 62 187 70 204
+rect 90 187 112 204
+rect 62 162 112 187
+rect 62 49 112 62
+<< polycont >>
+rect 70 187 90 204
+<< locali >>
+rect 0 507 175 554
+rect 0 468 33 507
+rect 141 468 175 507
+rect 0 456 175 468
+rect 33 416 62 429
+rect 33 240 38 416
+rect 56 240 62 416
+rect 33 229 62 240
+rect 112 416 141 429
+rect 112 240 119 416
+rect 137 240 141 416
+rect 112 229 141 240
+rect 62 204 98 212
+rect 62 187 70 204
+rect 90 187 98 204
+rect 62 179 98 187
+rect 33 150 62 162
+rect 33 74 38 150
+rect 56 74 62 150
+rect 33 62 62 74
+rect 112 150 141 162
+rect 112 74 119 150
+rect 137 74 141 150
+rect 112 62 141 74
+rect 0 22 175 25
+rect 0 3 15 22
+rect 160 3 175 22
+rect 0 0 175 3
+<< viali >>
+rect 33 468 141 507
+rect 38 240 56 416
+rect 119 240 137 416
+rect 70 187 90 204
+rect 38 74 56 150
+rect 119 74 137 150
+rect 15 3 160 22
+<< metal1 >>
+rect 0 507 175 554
+rect 0 468 33 507
+rect 141 468 175 507
+rect 0 456 175 468
+rect 33 416 62 456
+rect 33 240 38 416
+rect 56 240 62 416
+rect 33 229 62 240
+rect 112 416 141 429
+rect 112 240 119 416
+rect 137 240 141 416
+rect 112 215 141 240
+rect 0 204 98 215
+rect 0 187 70 204
+rect 90 187 98 204
+rect 0 176 98 187
+rect 112 176 175 215
+rect 33 150 62 162
+rect 33 74 38 150
+rect 56 74 62 150
+rect 33 25 62 74
+rect 112 150 141 176
+rect 112 74 119 150
+rect 137 74 141 150
+rect 112 62 141 74
+rect 0 22 175 25
+rect 0 3 15 22
+rect 160 3 175 22
+rect 0 0 175 3
+<< labels >>
+rlabel metal1 165 4 165 4 1 GND
+rlabel metal1 85 543 85 543 1 VDD
+rlabel metal1 8 185 8 185 1 IN
+rlabel metal1 153 188 153 188 1 OUT
+<< end >>
