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An Introduction to Verilog-A: Transitioning from Verilog Tutorial 1

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Lesson Plan (Tentative) Week 1: Transitioning from VHDL to Verilog, Introduction to Cryptography Week 2: A5 Cipher Implementaion, Transitioning from Verilog to Verilog-A Week 3: Verilog-A Mixer Analysis

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Analog Verilog (Verilog-AMS) Verilog introduced as IEEE Standard 1364 Dire need for analog circuits to be modelled as a language VHDL and Verilog come up with analog equivalents: AHDL and Verilog-AMS (Analog and Mixed Signal)

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New Types in Verilog-A Integer/Real (same as Verilog) Electrical (electrical wire) Parameter (parameter constants) Genvar (local variables eg for loops and such)

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Parameters Example: Parameter real gain = 1 from [1:1000]; Second keyword real specifies optional type (real or integer) From is used to specifies optional range of the parameter. [] is used to indicate that the end values are allowable while () means end values are not.

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Parameters Parameters cannot be changed at run time, but can be changed at compile time using defparam Example: module annotate; defparam tgate.m1.gate_width = 5e-6, tgate.m2.gate_width = 10e-6; endmodule

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Parameters Can also exclude ranges, eg Parameter real res = 1.0 from [0:inf) exclude (10:20) exclude 100; Can be arrayed, eg Parameter real poles[0:3] = {1.0, 2.0, 3.83, 4.0}; Can be strings, eg Parameter string type = “NPN” from { “NPN”, “PNP” };

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Operators Mostly same as Verilog, but has extra functions for analog design Built-in mathematical functions: –ln(x), log(x), exp(x), sqrt(x), min(x,y), max(x,y), abs(x), pow(x,y), floor(x), ceil(x) –sin(x), cos(x), tan(x), asin(x), acos(x), atan(x), sinh(x), cosh(x), tanh(x), asinh(x), acosh(x), atanh(x)

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Operators (con’t) Voltage/Current access: –V(b1), V(n1) access the branch voltage and node voltage wrt ground –V(n1,n2) accesses the difference between n1 and n2 –I(b1), I(n1) access the branch current and node current flowing to ground

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Operators (con’t) Voltage/Current access: –I(n1,n2) accesses the current flowing between n1 and n2 –I( ) accesses the current flowing into p1, a port

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Analog Operators (Filters) Cannot be placed in any loop or conditional (for, while, if, case, repeat) because internal state must be maintained Only in an analog block Argument list cannot be null

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Analog Operators ddt(x), calculates the time derivative of x idt(x,opt_ic), calculates the time integral of x (with or without initial condition) laplace_zp, laplace_zd, laplace_np, laplace_nd (various laplace transforms)

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Analog Operators Analysis types –Analysis() returns true(1) if analysis done is of that type (AC, DC, tran, noise, etc) Noise models –Can use white_noise, flicker_noise, noise_table

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User-Defined Functions Syntax: analog function real geomcalc; input l, w ; output area, perim ; real l, w, area, perim ; begin area = l * w ; perim = 2 * ( l + w ); end endfunction Called as follows: dummy = geomcalc(l-dl, w- dw, ar, per) ;

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Signals and Models Let’s take an example of a resistor (modelled as a voltage-controlled current source) module my_resistor(p,n); parameter real R=1; electrical p,n; branch (p,n) res; analog begin V(res) <+ R * I(res); end endmodule

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Signals and Models (con’t) Other current/voltage sources: –V(out) <+ A * V(in); //VCVS –I(out) <+ A * V(in); //VCCS –V(out) <+ A * I(in); //CCVS –I(out) <+ A * I(in); //CCCS

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Signals and Models RLC Circuit model –Series: V(p, n) <+ R*I(p, n) + L*ddt(I(p, n)) + idt(I(p, n))/C; –Parallel: I(p, n) <+ V(p, n)/R + C*ddt(V(p, n)) + idt(V(p, n))/L;

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Simple Amplifier Example: module amp(out, in); input in; output out; electrical out, in; parameter real Gain = 1; analog V(out) <+ Gain*V(in); endmodule

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Mixed Signal Models Example: one-bit DAC module onebit_dac (in, out); input in; inout out; wire in; electrical out; real x; analog begin if (in == 0) x = 0.0; else x = 3.0; V(out) <+ x; end endmodule Note that wires are used with electricals. The digital signals in this context are represented as bits

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Conclusions Verilog is so useful that it has been redesigned for analog/mixed signal applications Designer Guide (surprisingly easy to read) guide.org/VerilogAMS/VlogAMS-2.1- pub.pdf

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