Orban OPTIMOD-FM 5518, Operating Manual

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TECHNICAL DATA ORBAN MODEL 5518
The input reference waveform is converted to a square wave via IC505 and asso-
ciated circuitry, which implement a comparator with hysteresis. IC1103 is a CPLD
(complex programmable logic device) that accepts the reference square wave.
IC1001 is a PIC microcontroller that measures the frequency of the reference
square wave and (re)configures the CPLD as directed by the main microprocessor.
In turn, the CPLD works with IC1101, IC1102, and IC1104 to implement a phase-
locked loop to generate the system clocks. IC1104 is the phase comparator. The
single-order loop filter consists of R1100, R1106, R1107 and C1100. The 27 MHz
voltage-controlled oscillator IC1101 receives the output of the loop filter. The
output of IC1101 drives IC1102, which is a phase-locked loop frequency genera-
tor that locks to the 27 MHz output of IC1101 and generates four clock signals
from it. The four outputs of IC1102 are applied to the CPLD, which closes the
phase-locked loop as directed by the PIC and main microprocessor. The CPLD
generates the clocks (FCLK and BCLK) used by the DSP.
Output Circuits
This circuitry interfaces the DSP to the analog and digital audio outputs. The digital
audio from the DSP is transmitted to the digital-to-analog converter (D/A) and out-
put sample rate converter (SRC). The digital-to-analog (D/A) converter converts the
digital audio words generated by the DSP to analog audio. The analog output
stages scale and buffer the D/A output signal to drive the analog output XLR con-
nectors with a low impedance balanced output. The digital output transmitter ac-
cepts the digital audio words from the output sample rate converter (SRC) and
transmits them as AES3-format digital audio signals on the digital output connector.
1. Stereo Digital-to-Analog (D/A) Converter
Located on Input/Output/DSP board
The D/A, IC306, is a stereo, 24-bit delta-sigma converter. It receives the serial left
and right audio data samples from the DSP at 64 kHz sample rate and converts
them into audio signals requiring further, relatively undemanding analog filter-
ing.
2. Analog Output Stages
Located on Input/Output/DSP board
The left and right analog signals emerging from IC306 are each filtered, ampli-
fied, and applied to a floating-balanced integrated line driver, which has a 50

output impedance. The line driver outputs are applied to the RF-filtered left and
right analog output connectors. These analog signals can represent either the
transmitter or monitor output of audio processing.
Component-Level Description:
IC303 and associated components filter the left channel signal emerging from
IC306. The purpose of these stages is to reduce the out-of-band noise energy
resulting from the delta-sigma D/A’s noise-shaping filter and to translate the