Fundamentals-of-Microelectronics-Behzad-Razavi.pdf

Thus spice proves quite useful here labeling the

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Thus, SPICE proves quite useful here. Labeling the circuit in our mind, we write the netlist as: Step Response Example r1 in out 1k d1 out 0 is=1f, cjo=1p, vj=0.7 vin in 0 pulse(0 1 0 0.1n 0.1n 1) .tran 25p 3n .end As we encounter more sophisticated devices, the number of parameters that must be specified for their SPICE description increases, thereby making the task of netlist construction cumber- some and error-prone. For example, today’s MOSFETs require hundreds of parameters in their SPICE descriptions. To avoid repeating the parameters for each element, SPICE allows the defi- nition of “models.” For example, the above diode line can be written as d1 in out mymodel .model mymodel d (is=1f, cjo=1p, vj=0.7) Note that f stands for femto and not for farad. That is, a capacitor expressed as 1f in SPICE description assumes a value of 1 fF.
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BR Wiley/Razavi/ Fundamentals of Microelectronics [Razavi.cls v. 2006] June 30, 2007 at 13:42 827 (1) Sec. A.3 Element Descriptions 827 Upon reaching the fourth entry in the diode line, SPICE recognizes that this is not a value , but a model name and hence seeks a .model command that defines the details of “mymodel.” The letter “d” in the .model line specifies a diode model. As seen below, this letter is replaced with “npn” for an bipolar transistor and “nmos” for an NMOS device. Example A.9 Plot the input/output characteristic of the circuit shown in Fig. A.12(a). Assume and follow the above diode model. D 1 D 2 in V out V 1 k Figure A.12 Solution Labeling the circuit in our mind, we write the netlist as: Diode Circuit d1 in out mymodel d2 out in mymodel r1 out 0 1k vin in 0 dc 1 .dc vin -3 +3 2m .end A.3.3 Bipolar Transistors The definition of bipolar transistors requires special attention to the order of the terminals. Con- sider the example shown in Fig. A.13, where is expressed as: V CC 1 k = 2.5 V emi in out 100 Q 1 Figure A.13 Common-emitter stage. Collector Base Emitter Substrate Model q1 out in emi 0 bimod where the device name begins with the letter q to indicate a bipolar transistor, and the first four nodes represent the collector, base, emitter, and substrate terminals, respectively. (In most cases,
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BR Wiley/Razavi/ Fundamentals of Microelectronics [Razavi.cls v. 2006] June 30, 2007 at 13:42 828 (1) 828 App. A Introduction to SPICE the substrate of transistors is tied to ground.) As with diodes, the parameters of the transistor are expressed in a model called, for example, bimod: .model bimod npn (beta=100, is=10f) Example A.10 Construct the SPICE netlist for the circuit of Fig. A.13. Assume the input must be swept from 0.8 V to 0.9 V. Solution The netlist is as follows: Simple CE Stage q1 out in emi 0 bimod remi emi 0 100 rout out vcc 1k vcc vcc 0 2.5 vin in 0 dc 1 .dc 0.8 0.9 1m .model bimod npn (beta=100, is=10f) .end Two observations prove useful here. (1) The two resistors are labeled according to the nodes to which they are attached. This approach allows us to find each resistor more readily than if it is simply labeled by a number, e.g., r1. (2) In the above netlist, the term “vcc” refers to two distinct
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