Block Diagrams Descriptions; Receiver Path - Motorola MTM800 User Manual

THEORY OF OPERATION (TRANSCEIVER)

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.
Antenna
Harmonic
Filter
Dynamic
Range
Extension
16.8 MHz
Reference
from FGU
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.
Switch
Rx
Tx Pre-selector
From Tx PA
nd
2
Mixer
LNA
Variable
Gain
Amplifier
nd
2 LO
PLL
nd
Loop
2
LO
Filter
Figure 4.1-2
st
1
Image
LNA
Filter
Decimation
ADC
Filter
Sample
Clock
IF Digitizing
PLL
Subsystem
Loop
Sample
Clock
Filter
VCO
Receive Path Block Diagram
LO From
FGU
IF
73.35 MHz
Mixer
Amplifier
First IF Filter
Formatting DSP (Part of
SSI Controller)
(BBP)
4.1 - 5
CODEC
AUDIO
PA