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Optimization With HSpice. Before you start optimizing. What are you optimizing for? Linearity (as in an amplifier) Gain Frequency response Drive ability Transition point Speed. Before you start optimizing. How are you going to test the design’s quality? Simulated loading Resistive
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Before you start optimizing • What are you optimizing for? • Linearity (as in an amplifier) • Gain • Frequency response • Drive ability • Transition point • Speed
Before you start optimizing • How are you going to test the design’s quality? • Simulated loading • Resistive • Capacitive • Both • In circuit testing
Optimization syntax • The HSpice manual is located in ~cg477/tools/hspice/98/98.4/docs • The syntax is described in detail in chapter 12 • This is a brief introduction • I will show examples afterwards
Optimization statements • .MODEL modelname OPT optimization parameters • .PARAM parameter=OPTxxx(optimization range specification) • .DC, .AC, or .TRANS statement with MODEL=modelname, OPT=OPTxxx, and RESULTS=measurename(s) • .MEASURE statement with GOAL specified
Limitations • You can optimize transistor sizes to shift transition points, gain, linearity, etc. • Transistor optimization is difficult even for HSpice. My experience has been that it is mostly useful for aiding in sizing. • HSpice is very useful for bias voltage determination. • If you are close to the best choice for an optimization parameter, HSpice will have difficulty finding that best choice. It can get you close, however.
Example: buffer • ************************ • .MODEL model1 OPT ITROPT=30 • .PARAM TransP=OPT1 (16, 4, 50, 1) • .PARAM TransN=OPT1 (27, 4, 50, 1) • .DC Va 0V 3.3V 0.0001 SWEEP OPTIMIZE=OPT1 RESULTS=transpt MODEL=model1 • ************************ • .DC Va 0 3.3 0.001 • .MEASURE DC transpt WHEN v(q0)=v(a) CROSS=LAST goal=1.2 • * other hspice commands • m1000 vdd a q0 vdd pch w=TransP l=2 • + ad=96 pd=44 as=80 ps=42 • m1001 q1 q0 vdd vdd pch w=TransP l=2 • + ad=80 pd=42 as=0 ps=0 • m1002 gnd a q0 gnd nch w=TransN l=2 • + ad=138 pd=150 as=115 ps=102 • m1003 q1 q0 gnd gnd nch w=TransN l=2 • + ad=115 pd=102 as=0 ps=0
Examples: gain 2 amplifier • ******************************************** • .MODEL model1 OPT ITROPT=30 • .PARAM Pbv1=OPT1 (3.233, 0.00, 3.30) Pbv2=OPT1 (0.932, 0.00, 3.30) • *.PARAM Tbv1=OPT1 (28, 3, 50, 1) Tbv2=OPT1 (29, 3, 50, 1) • .PARAM Tbv1=25 • .PARAM Tbv2=44 • .PARAM Tain=58 • .param trans_pt=trans_pt_low • .DC Vain 0.5V 2.50V 0.001 SWEEP OPTIMIZE=OPT1 RESULTS=slope_mid,curve_area MODEL=model1 • ******************************************** • .param slope_cur="-sqrt(2)" • .param trans_pt_low=1.150 • .param trans_pt_high=1.250 • .param interval_low="trans_pt-(trans_pt_high-trans_pt_low)/2" • .param interval_high="trans_pt+(trans_pt_high-trans_pt_low)/2" • .param interval_low_mid="(trans_pt+interval_low)/2" • .param interval_high_mid="(trans_pt+interval_high)/2" • .param interval_center="trans_pt-sign((trans_pt_high-trans_pt_low)/2,trans_pt-(trans_pt_high+trans_pt_low)/2)" • .meas DC slope_mid deriv v(t1) at=trans_pt goal=slope_cur weight=200 • .param ideal_curve(vin)= "slope_cur*(vin-trans_pt)+trans_pt" • .meas DC curve_area integ par("v(t1)-ideal_curve(v(ain))") from=interval_low to=interval_high goal=0.0001 • * additional spice statements are here (but not applicable to this example) • m1000 t1 bv1 Vdd GND nch w=Tbv1 l=2 • + ad=431 pd=420 as=250 ps=220 • m1001 t1 bv2 GND GND nch w=Tbv2 l=2 • + ad=0 pd=0 as=788 ps=732 • m1002 GND ain t1 GND nch w=Tain l=2 • + ad=0 pd=0 as=0 ps=0
