Motorola MC92303BT Datasheet
MOTOROLA
SEMICONDUCTOR TECHNICAL DATA
Product Brief
QPSK/BPSK DIGITAL DEMODULATOR
Current Information@www.mot.com/ADC
MC92303
The MC92303 is a coherent digital demodulator for QPSK and BPSK modulated
signals utilized in Digital-TV applications according to the EBU defined DVB transmission standard for satellite Set-Top systems or similar. The MC92303 contains all the
functionality required to lock onto signals with frequency offsets as large as the baud
rate and extract the desired signal from a frequency band with adjacent channel interference and other undesirable signals.
Feature Summary
• DVB compliant QPSK/BPSK Coherent Demodulator
• Variable Modulation Rate up to 30 MBaud to work with all present European DVB
Channels
• Selectable Input Format (Offset Binary/2’s Complement)
• DC Offset Removal, I/Q-swapping and Input Format Selection in one block
• Decimation Filters for Oversampling Ratios of 2/T, 3/T, 4/T, 6/T, 8/T, 12/T and 16/T
• Half Nyquist Baseband Filters (α=0.35)
• Internal Numerically Controlled Oscillator (NCO)
• Automatic Gain Control (AGC) provided to analog front-end
• Automatic Frequency Control (AFC) to ±Rs (Symbol Rate)
• Clock Synchronization with 1-Bit Σ∆-Converter Output for ADC control
• Programmable Second Order Loop Filters for Carrier Recovery and AGC
• 3-bit Soft Decision output per Symbol with selectable format (Offset Binary/2’s
Complement/Sign Magnitude)
• Programmable Sampling Rates of the Digital Sigma-Delta Converters
• < 0.5 dB Implementation Loss from theory
•I2C Programmable Interface
• 0.5µ CMOS Process at 3.3V
RESET
I,Q[5:0]
CLK_VCO
FORMAT
SDA
SADR[6:0]
SCL
CLK
VCO
AGC
Q_soft[2:0]
I_soft[2:0]
Ordering Information
Device
MC92303BT
Package
160QFP
AGC
Control
I
Q
SDA
SCL
SADR
Σ∆
6
6
7
DC-
Removal
2
C
I
Interface
Parameters
AGC
Loop Filter
cosΘ
Complex
Multiplier
sinΘ
NCO
Decimation
Filter
Digital AGC
Sweep /
Carrier
Loop Filter
Ext. Clkref.
Half Nyquist
False Lock Detector
Phase Lock Detector
Filter
AFC / Clock
Synchron.
Σ∆
8/3 Bit Mapper
Data
Estimator
VCO
Control
3
I_soft
3
Q_soft
Figure 1. QPSK/BPSK Demodulator Block Diagram
This document contains information on a new product.
Specifications and information herein are subject to change without notice.
MOTOROLA, INC. 1997 4/10/97
Control Loops
The inputs to the device are 6 bit I and Q digital
signals. A pin programmable input format selector allows use of A/D converters with either offset binary or
2’s complement output format. The A/D output data is
fed into the carrier synchronization loop which is capable of locking onto signals with frequency offsets as
large as the baud rate. The carrier synchronizer includes a complex multiplier, a phase detector, a programmable second order loop filter, a phase lock
detector, a false lock detector and a frequency sweep
function. The carrier tracking loop is closed digitally using an internal numerically controlled oscillator (NCO).
The frequency sweep rate, the frequency sweep limit,
the phase and frequency lock detector thresholds and
the loop parameters are programmable. The I and Q
QPSK symbols produced in this loop are further processed by a Decimation Filter and a Half Nyquist Filter
(roll-off factor of 0.35) to perform the matched filtering.
Once processed, the filtered data samples are passed
to the data estimator which produces 3 bits of I and Q
soft decision data (device output) as well as I and Q error vectors.
The demodulator also performs a non-coherent
automatic gain control (AGC) function on the IF signal
using a total power algorithm and generates a single bit
output signal which must be lowpass filtered and interfaced to the gain control port of a variable gain amplifier. The AGC includes a programmable second order
loop filter.
Another control loop, the mid-symbol sampling
synchronization loop, ensures that the optimum A/D
sampling times are determined by providing a single bit
output signal to a voltage controlled oscillator (VCO)
clock generator. This VCO quiescent frequency is automatically set to 2, 3, 4, 6, 8,12 or 16 Rs depending on
from LNB
1st IF Freq.
0.95 - 2.15 GHz
Freq.
Synthesizer
2nd IF Freq.
480 MHz
0°
90°
the oversampling factor. Its output signal levels must be
suitable for clocking both the A/D converter and the
QPSK demodulator.
Decimation Filter
The Decimation Filter block consists of three switchable decimation filters: two 1/2-band filters and a 2/3band filter. Together with a switchable input decimation
of 2, the decimation filter block enables the demodulator to operate at an oversampling ratio of 2, 3, 4, 6, 8,
12, or 16. The variable sampling demodulator minimizes the external components to build a Set Top box for
the whole range of data rates. In order to compensate
different signal gains after the decimation an internal
Digital AGC produces a control signal which adjusts the
gain after the complex multiplier.
I2C interface
The MC92303 is a slaved device that is intended
to be controlled via the I2C interface. In accordance
with the I2C specification, the I2C master initiates all
data transfers to and from the demodulator and provides the I2C clock. Data is always transferred one byte
at a time, MSB first, and the receiver must acknowledge
each byte by pulling the data line low during the cycle
following the LSB. The demodulator interprets the byte
following its slave address as an 8-bit sub-address
which selects a particular register to be written to or
read from.
Application
The demodulator can be used to implement a DVB
compliant demodulator with the circuitry shown in Figure 2. The 3 bit soft decision data of the demodulator is
connected directly toa Viterbi Decoder or a combined
Viterbi and Reed Solomon Decoder.
Host
CPU
MC92302
VI1[2:0]
DO[7:0]
VI0[2:0]
Freq. = 0 Hz
LO
Clock
VCO
A
A
D
D
VCO
I[5:0]
SDA
I_soft[2:0]
MC92303
Q_soft[2:0]
Q[5:0]
AGC
2
I
C
Figure 2. DVB Application Example
MOTOROLA MC92303
2 Rev.1.3
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