Download - Wolfram Research

162 2. Tutorial
Let’s examine the effects of the preceding parameter definitions and assignments by recalculating the
single-input-to-single-ended voltage transfer function of the differential amplifier, this time using the
high-frequency MOS model we just defined. First, we set up symbolic circuit equations using the
option setting DefaultSelector −> HighFrequency.
In[38]:= eqscmoshf = CircuitEquations[cmosdiffamp,
ElementValues −> Symbolic,
DefaultSelector −> HighFrequency]
Out[38]= DAEAC, 9 9
As a result of default parameter instantiation (see Chapter 2.3) unique symbolic values have been
generated for all instances of the transistor model elements. In addition, the arguments of the Value
keywords have been replaced by the numerical values specified in the model references. Therefore,
we can now use GetDesignPoint to extract the design-point list from the DAEObject.
In[39]:= GetDesignPoint[eqscmoshf]
Out[39]=
V2 0.0001, V1 1., CL 1. 10 13 , Cgs$M3 2.38 10 13 ,
Cgd$M3 0., gm$M3 0.0000654, Gds$M3 7.89 10 7 ,
gmb$M3 0.0000217, Cbd$M3 0., Cbs$M3 0., Cgs$M4 2.38 10 13 ,
Cgd$M4 0., gm$M4 0.0000654, Gds$M4 7.89 10 7 ,
gmb$M4 0.0000217, Cbd$M4 0., Cbs$M4 0., Cgs$M1 2.33 10 13 ,
Cgd$M1 0., gm$M1 0.0000596, Gds$M1 3.01 10 7 ,
gmb$M1 0.0000441, Cbd$M1 0., Cbs$M1 0., Cgs$M2 2.33 10 13 ,
Cgd$M2 0., gm$M2 0.0000596, Gds$M2 3.01 10 7 ,
gmb$M2 0.0000441, Cbd$M2 0., Cbs$M2 0., Simulator PSpice
2.9.7 AC Analysis of the CMOS Amplifier
To conclude this chapter let’s carry out an AC analysis of the CMOS amplifier. Our task shall be
to determine a symbolic formula which approximates the frequency response of the voltage gain
to first order. We begin with importing the numerical data from the PSpice small-signal simulation
applying the Analog Insydes command ReadSimulationData (Section 3.10.3). Note that we have to
specify the simulator-specific option setting Simulator −> "PSpice".
In[40]:= data = ReadSimulationData[
"AnalogInsydes/DemoFiles/CMOSdiffamp.csd",
Simulator −> "PSpice"]
Out[40]=
V5 InterpolatingFunction1., 1. 10 9 ,
In[41]:= tfcmosPSpice := "V(5)" /. First[data]
The Bode diagram of the simulation result shows that the transfer function has a dominant pole
which is responsible for the corner in the magnitude response at MHz.