Tài liệu ANALOG BEHAVIORAL MODELING WITH THE VERILOG-A LANGUAGE- P6 doc

Voltage Regulator

180 degrees Celsius is shown in Figure 5.16. The “bow” in the voltage with respect to

temperature is a typical characteristic for bandgap based voltage reference.

Figure 5.17, shows the output voltage and the cell current as the supply voltage is var￾ied over the expected range of usage from 4 to 6 volts.

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Figure 5.18, testing the dynamic response of models, verifies the output voltage as a

function of the switch current between the reference and the buffer amplifier.

136 Verilog-A HDL

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QPSK Modulator/Demodulator

5.5 QPSK Modulator/Demodulator

Quadrature phase-shift keying, or QPSK, is an example of a modulation technique in

which the information carried within the signal is contained in the phase. The phase

of the signal can take on one of four values, such as shown in the constellation dia￾gram of Figure 5.19.

5.5.1 Modulator

As shown in the QPSK modulator schematic (Figure 5.20), the incoming binary

sequence is transformed into polar form by a nonreturn-to-zero (NRZ) encoder. Here,

the binary 1 and 0 symbols are transformed into +1 and -1 respectively. The NRZ data

stream is de-multiplexed into two separate binary sequences consisting of the odd￾and even-numbered input bits. These binary sequences are used to modulate a pair of

quadrature carriers, which are added together to produce the QPSK signal.

The QPSK modulator module consists of two primary components for the polariza￾tion of the input data sequence and the modulation of the quadrature components to

produce the QPSK signal. The modulator samples the input data stream (0s and 1s)

and converts it to the corresponding -1 or +1 every period seconds using the

timer operator. An integer variable state is toggled to convert the serial data

stream into two parallel streams for modulating the quadrature carriers.

LISTING 5.12 Verilog-A module definition of QPSK modulator

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