Goal Functions — Inverter Analysis

We will use the circuit of the previous section and find the noise margins (NMH and NML) and input and output transition voltages (Vil, Vih, V0l, V0h)- The transfer function of the NMOS inverter of the previous section was found on page 225, and is repeated below with approximate values of VIL, Vih, Vql, V0h shown on the plot  

The name of the function is Voh. It has 2 input arguments (1,2). The first input will be the derivative of the trace, and the second input will be the trace itself. To use this function we would type Voh(d(V(Vo)), V(Vo)), where d(V(Vo)) is the derivative of the output trace and V(Vo) is the output trace. 1 search forward level means search the first input forward and find a level. The level we are looking for is -1. When the point is found, the text 1 designates its coordinates as xl and yl. Since the first input is the derivative of the trace, 11 search forward level (-1) 11 finds where the slope of the trace is -1. 2 search forward xvalue(xl) 2 searches the second input forward and finds the point when the x-coordinate is equal to x1. This point is where the slope of the transfer curve is -1. 12 marks the coordinates of this point as x2 and y2. The function returns the y-coordinate of this point Voh(1,2)=y2, which is equal to V0h-A second function is  

This function is similar to Voh except that it returns the x-coordinate of the point where the slope is -1. The x-cooidinate of the point where the slope is -1 is our definition of Vil. 

This function is used to find V0l and is similar to the Voh function. Note that Vol is also defined where the slope of the transfer curve is -1. To distinguish V0h and V0l. this function finds the point starting from the end of the trace and searching backwards. There are two points on the trace where the slope is -1. This function finds the point closest to the end of the trace. 

The goal functions are used in Probe. Follow the procedure of Section 4.D.3. When you obtain the Probe plot of the transfer curve V(Vo) versus V Vin below, continue with this section  

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