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Nexxim Simulator >
Nexxim Component Models >
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   Voltage Source, QAM Modulated       

Voltage Source, QAM Modulated

 

QAM Modulated Voltage Source Netlist Form

The netlist format for a Quadrature-Amplitude modulated (QAM) voltage signal generator is:

Axxxx n+ n- [M=val] [FB=val] [D=val]
SEED=val [BITLIST=#bitlist] [BITFILE=file_reference]
[UPCHOICE=val] [UPFACTOR=val]
[V=val] [VO=val]
[ALPHA=val] [THETA=val] [TONE=val]
[FILTCHOICE=val] [NTAPS=val]
[ROLLOFF=val] [NORMALIZESCHEME=val] [BT=val]
[FC=val] [TD=val]
[NOISEVEC=[f1,psd1, ... fn,psdn]]
COMPONENT=qam_iq_source

n+ and n- are the positive and negative nodes. The brackets shown in bold are required.

The entry COMPONENT=qam_iq_source is required.

The QAM modulated signal generator can be used as a source of data for Nexxim envelope analysis. See Envelope Analysis for details.

Note 

The QAM source supports only square constellations. Parameter M (number of constellation points) must be a power of 2.

 


QAM-Modulated Voltage Source Parameters

Parameter

Description

Unit

Default

M

Number of points in constellation (2=binary, 4=quaternary) Must be a power of 2 (square constellation)

None

4

D

Spacing between constellation points

Volt

2

SEED

Integer seed for random pattern [Must be greater than 0.0]

None

None

BITFILE

Reference to external file with the bit values

None

None

BITLIST

Explicit list of bits to generate

None

None

FB

Data rate

Bits/Second

1.2288e6

ALPHA

Damping factor

Second-1

0.0

THETA

Phase delay

Degree

0.0

TD

Time delay to start of first waveform, and to start of first repeat

Second

0.0

V

Output voltage

Volt

None

VO

Voltage offset

Volt

0.0

UPCHOICE

Upsampling technique.

1 = Zero insertion

0 = Sample repeat

None

1

UPFACTOR

Upsampling factor

None

10

TONE

Frequency to use for harmonic balance analysis. Should be the same as FC.

Hertz

0.0

FC

Carrier frequency

Hertz

1e9

FILTCHOICE

Low pass filter selector

1 = No filter

2 = Spectral raised cosine (SRC)

3 = Square root spectral raised cosine (SRRC)

4 = Rectangular (REC)

5 = Gaussian GAUSS)

None

1

NTAPS

Number of filter taps

None

31

NORMALIZESCHEME

Normalization method for tap coefficients (weights)

1 = No normalization

2 = Maximum sum (amplitude) of coefficients is 1

3 = L1 norm of coefficients is 1

4 = L2 norm of coefficients is 1

None

1

ROLLOFF

Controls the excess bandwidth parameter for SRC and SRRC filters (0< ROLLOFF <1)

None

0.35

BT

Bandwidth-time product, for FILTCHOICE=5 (GAUSS)

None

0.25

NOISEVEC

List of shot noise frequencies (f1...fn) and corresponding noise power spectral densities (psd1...psdn), in pairs.

The sequence of frequencies must be monotonically non-decreasing.

Hertz,
Volt2/Hertz

None

PSK-Modulated Voltage Source Netlist Example

Aqamtest 23 53 BITFILE='C:/qamdatadirectory/qamdata.txt’ FC=2.5e9 COMPONENT=qam_iq_source

Notes

1. When no BITLIST or BITFILE argument is supplied, the QAM voltage source generates a pseudorandom bit sequence, starting from a random seed value. When no BITLIST or BITFILE is present, the optional SEED can be used to control the bit sequence. The SEED must be an integer value (the maximum absolute value is the maximum size of integers on your system). Using the same SEED guarantees that the same sequence of bits will be generated on each simulation.

2. When a BITLIST or BITFILE is supplied, the QAM source generates the specified sequence of 0 and 1 bits, and repeats the sequence until simulation terminates. When a BITLIST or BITFILE is present, any SEED value will be ignored. If two or all three of BITFILE, BITLIST, and SEED are present, Nexxim uses the precedence order: BITFILE > BITLIST > SEED.

3. In all cases, the sequence of generated bits starts after the time delay given by TD, and continues until the stop time (tstop) of the transient analysis is reached.

4. The parameters BITFILE =file_reference and NOISEVEC =file_reference refer to external files containing the data. See File References in the Nexxim Netlist File Format topic for details.

5. For harmonic balance analysis, the test tones must be submultiples or equal to the frequencies of the actual voltage or current inputs to the circuit. To ensure that the desired HB frequency is used with a QAM source, qualify the source by adding a TONE=tone_val entry at the end of the instance statement. The tone_val is then used in a subsequent HB statement.

 

 



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