Motorola MTM800 - Block Diagrams Descriptions; Receiver Path

THEORY OF OPERATION (TRANSCEIVER) 4.1 - 5
Block Diagrams Descriptions
The block diagrams descriptions cover Receiver Path, Transmitter Path, Frequency Generation
Section, and Controller Section.
Receiver Path
The received signal (see figure below) from the antenna is directed by the Antenna Switch to the
Front End Pre-selector Filter.
Figure 4.1-2 Receive Path Block Diagram
The receive pre-selector filter performs the following functions:
• passes frequencies in the 851 – 870 MHz receive frequency range, and
• blocks unwanted spurious frequencies like half IF and image frequencies.
The signal is mixed with the low side injection local oscillator signal to create the first IF at 73.35
MHz. The IF signal is filtered by the crystal filter, amplified by the IF amplifier, and sent to the IF
Digitizing IC.
The IF Digitizing Subsystem performs the following functions:
• down conversion to the second IF at 2.25 MHz,
• perform a bandpass sigma-delta analog-to-digital conversion of the second IF signal into in-
phase (I) and quadrature (Q) digital signals.
Antenna
Switch
From Tx PA
DSP (Part of
Controller)
2
nd
Mixer
1
st
LO From
FGU
LNA
2
nd
LO
ADC
Loop
Filter
Loop
Filter
2
nd
LO
PLL
Variable
Gain
Amplifier
Formatting
SSI
(BBP)
IF Digitizing
Subsystem
16.8 MHz
Reference
from FGU
Sample
Clock
PLL
Tx
Rx
Dynamic
Range
Extension
Decimation
Filter
Image
Filter
Mixer
73.35 MHz
First IF Filter
IF
Amplifier
Harmonic
Filter
LNA
Pre-selector
CODEC
AUDIO
PA
Sample
Clock
VCO
6866539D31.book Page 5 Tuesday, March 20, 2007 6:32 PM