13.1 ABM Devices

The extended sources provide five additional functions which are defined as:

Fig. 13.1 shows a typical use of an ABM EValue device to implement a voltage doubler. The ABM has a differential input (IN +, IN −) and a double-ended output (OUT +, OUT −). When you first place the ABM, the default expression is given by

V(%IN +, %IN −)

which calculates the difference between the voltages on the input pins IN + and IN −. In order to multiply by a factor of 2, the expression is first enclosed in curly brackets (braces).

2⁎{V(%IN +, %IN −)}

Fig. 13.2 shows the output voltage when a 1 V sinewave is applied to the input pins.

Other mathematical functions that can be applied to ABM expressions are shown in Table 13.1.

Conditional statements can also be applied to ABM parts. For example, in Fig. 13.3, if the input voltage is greater than 4 V, then output 0 V else output 5 V. This effectively is a comparator. The resulting waveform is shown in Fig. 13.4.

The first-order 159 Hz low pass filter in Fig. 13.5 can be defined by the transfer function:

$\frac{V_{\text{out}}}{V_{\text{in}}}=\frac{1}{1+j\frac{\omega }{{\omega }_{\mathrm{c}}}}$

where the cut off frequency is given by

${\omega }_{\mathrm{c}}=\frac{1}{\mathit{CR}}=2\mathit{\pi f}$

$f=\frac{1}{2\mathit{\pi CR}}=\frac{1}{2\pi \times {10}^{-6}\times {10}^3}=159\mathrm{Hz}$

Fig. 13.6 shows the frequency response of the filter.

Laplace ABM's can be used to implement filter circuits where the transfer function is transformed to the s domain where s = jω and ω = 2πf so the transfer function for the low pass filter is defined in the s domain by

$\frac{V_{\text{out}}}{V_{\text{in}}}=\frac{1}{1+\mathit{s\tau }}$

where

$\tau =\mathit{CR}={10}^{-6}\times {10}^3$

$\tau ={10}^{-3}\text{or}0.001s$

The filter circuit is redrawn in Fig. 13.7 with the transfer function given as:

$\frac{V_{\text{out}}}{V_{\text{in}}}=\frac{1}{1+{0.001}^{\ast }s}$

Fig. 13.8 shows the low pass frequency response for the filter.

In the circuit of Fig. 13.9, both inputs are grounded but the ABM expression is referencing a net name called “source.” This is useful to reduce the wiring complexity of a circuit especially if there are multiple ABM's being driven by a single source. Note that since a GValue ABM part is being used, the output is a current and therefore cannot be left unconnected. Hence the output resistor provides a DC path to 0 V.

In version 17.2, two new behavioral delay functions have been introduced, DelayT() and DelayT1(). Both these functions have improved simulation times and more efficient handling of convergence issues compared to the standard delay functions such as TLINE. DelayT() requires two parameters, delay time and max delay, whereas DelayT1() only requires the delay value and also inverts the input signal. The delay functions are shown in Fig. 13.10 and can be found in the function.olb library in the advanced analysis folder.

In later software versions you can search for the delay functions using:

Place > PSpice Component > Search

Then under Categories, select Analog Behavioral Models > General Purpose as shown in Fig. 13.11.