Glenayre Electronics Inc. GL-T8600-CN Manual Do Utilizador
Glenayre Document Number: 9110.00172
DSP Exciter
Issue 1, Rev. I: 01/15/97
THEORY OF OPERATION
Print Date: 02/19/97
Copyright © 1997 Glenayre
Page: 6-5
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to the IF stage circuit. To produce the first IF signal, the DSP modulator contains two DSPs
(a signal modulator and a quadrature modulator), a digital-to-analog converter, and a read-
only memory. The following text describes these four components and their signal flow.
(a signal modulator and a quadrature modulator), a digital-to-analog converter, and a read-
only memory. The following text describes these four components and their signal flow.
6.3.2.1
Digital Signal Modulator
The signal modulator (SM) generates modulation that contains the paging information,
which is supplied by digitized audio or FSK data. The digitized audio is input into a serial
input port. An external edge detector is required to input the FSK data. The SM converts
one of the data inputs into a modulated signal, which is mathematically represented within
the SM as a vector signal, defined by its rectangular coordinates. These coordinates,
commonly known as I and Q, are supplied to the digital quadrature modulator as 16-bit
parallel data. The modulated signal output from the SM depends on the following signal
characteristics:
which is supplied by digitized audio or FSK data. The digitized audio is input into a serial
input port. An external edge detector is required to input the FSK data. The SM converts
one of the data inputs into a modulated signal, which is mathematically represented within
the SM as a vector signal, defined by its rectangular coordinates. These coordinates,
commonly known as I and Q, are supplied to the digital quadrature modulator as 16-bit
parallel data. The modulated signal output from the SM depends on the following signal
characteristics:
•
modulation scheme
•
frequency response or rise time
•
input logic or data inversion
•
deviation level or bandwidth
•
offset from carrier frequency
•
analog gain and deviation limit
The SM also performs all communications between the DSP modulator circuit and the
MCU control circuit. These communications are through the SM 16-bit parallel data port.
External input and output latches expand the capabilities of this port. Control inputs consist
of commands such as reset, request status, set paging signal parameter, change mode, and
boot program. Requested status outputs consist of current mode, deviation levels, input
level, input gain, modulation detected, and current polarity. Nonrequested status outputs
indicate the existence of analog limiting and modulation.
MCU control circuit. These communications are through the SM 16-bit parallel data port.
External input and output latches expand the capabilities of this port. Control inputs consist
of commands such as reset, request status, set paging signal parameter, change mode, and
boot program. Requested status outputs consist of current mode, deviation levels, input
level, input gain, modulation detected, and current polarity. Nonrequested status outputs
indicate the existence of analog limiting and modulation.
6.3.2.2
Digital Quadrature Modulator
The digital quadrature modulator (DQM) performs interpolation and up-conversion of the
modulated signal. The modulated signal input to the DQM is applied by the SM as I and Q
components (16-bit parallel data). The DQM performs trigonometric computations at a
much higher sampling rate, which determines the first IF signal value and frequency. The
modulated signal output from the DQM is supplied from its serial data port to the D/A
converter.
modulated signal. The modulated signal input to the DQM is applied by the SM as I and Q
components (16-bit parallel data). The DQM performs trigonometric computations at a
much higher sampling rate, which determines the first IF signal value and frequency. The
modulated signal output from the DQM is supplied from its serial data port to the D/A
converter.
6.3.2.3
Digital-to-Analog Converter
The digital input to the digital-to-analog (D/A) converter is the modulated signal from the
DQM. This data arrives as serial data. The analog output from the D/A converter is the first
IF signal. In addition to the IF stage circuit, the first IF signal is supplied to the MCU
control circuit, where it is rectified and filtered to generate fault logic.
DQM. This data arrives as serial data. The analog output from the D/A converter is the first
IF signal. In addition to the IF stage circuit, the first IF signal is supplied to the MCU
control circuit, where it is rectified and filtered to generate fault logic.