The delay macro is designed to provide a simple time delay element in transient analysis or a phase shift in AC analysis. This macro is designed to be used with analog circuitry. There is a digital delay line primitive that offers the same function for digital circuits. This macro is preferred for analog circuits for two reasons: 1) the digital delay line would need I/O models if connected to analog components, which would use more components than the analog macro and force the output of the delay line to the analog voltage equivalent of digital states, and 2) the digital delay line has no AC equivalent whereas this macro will produce a phase shift. The delay macro appears in the figure below.
The single parameter in the macro is delay. This parameter defines the time delay that the macro will produce. The macro consists of two resistors, two VofV dependent sources, and an ideal transmission line. The two VofV dependent sources are used as buffering for the transmission line. The ideal transmission line is defined with a characteristic impedance of 50 ohms and a time delay that will be defined by the delay parameter. There is a 50 ohm termination resistor at the output of the transmission line to match the characteristic impedance of the line. This insures that the input waveform is passed cleanly through to the output without any reflections from the line. The 1E9 resistor is used to provide a DC path to ground at the input.
The settings in the Component Editor for the Delay macro need to be defined. The component has been added to the Macros group in the Analog Primitives section. The name has been defined as Delay in order to match up to the macro circuit which is called Delay.cir. The shape used is Dlyline which is an existing shape in the shape library. The definition for the component is Macro. The pins have been defined as analog pins with the names In and Out. These pin names must match exactly with the node names in the macro circuit.
The test circuit for this macro is simply a 1Mhz sine wave going into the input of the Delay macro. The macro has been defined with the VALUE attribute of:
Delay(100n)
to provide a 100ns delay for the sine wave. Below is a plot of the input and output waveforms of the macro. The input waveform is passed cleanly through the macro with a 100ns shift at the output. The final figure is an AC analysis plot of the phase at the output of the macro for the same circuit. The phase values at 1MHz and 10MHz are shown in the cursor information. The 100ns delay is 10% of the period at 1MHz and 100% of the period at 10MHz. The macro produces the correct phase shifts of -36 degrees and -360 degrees at these frequencies.
