Roadrunner Ic (Rx Path); Frequency Generator (Rf) Section - Motorola i425e Detailed Service Manual

OVERVIEW: iDEN Digital Modulation Technology

1.7.3 Roadrunner IC (RX Path)

The Roadrunner IC performs the digital conversion, digital filtering, and the AGC control of the
ra dio. The main function of the IC, from an RX perspective is the A/D conversion performed by
the Sigma Delta converter. This digitized output signal is processed by FIR and IIR filtering and
then the final output is framed and sent to the Baseband Processor via the Receive Synchronou
Serial Interface Bus.
The Roadrunner also controls both the RF step attenuators and the continuous AGC control lin
The RF step attenuator is enabled when the Roadrun
e nable the attenuator. This occurs when the unit receives a desired signal stronger than -50dBm.
The continuous AGC functionality is controlled by an analog voltage line which feeds the LNA
module. This voltage ranges from approximately 1.3875
signals greater than ~-60dBm at the antenna input.
1.8 F requency Generator (RF) Section
This sec tio contains the following main components of the R n
TCXO based reference oscillator circuit.
Host system clock synthesizer.
(Sledgehamm
Main/RX Voltage Controlled Oscillator (VCO).
Note: The main RX VCO output is used to source to main prescaler input of SLEDGEHAM
main synthesizer PLL.
A ll iDEN frequ encies in the i425/i290 originate from the 33.6 MHz reference frequency generated
b y Sledgehammer synthesizer and TCXO (Y600) reference oscillator circuit. The TCXO
g enerates a 33.6 MHz signal, which is temperature compensated. Error! Reference source not
und. illustrates the frequency generation circuitry path.
fo
32
er) Phase Locked Loop synthesizers (Main & Escort).
Figure 11: iDEN Frequency Generat
ner logic line signals the LNA module to
V to 2.5 V and increases linearly for
F board:
or Circuitry
s
es.
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6880401P26-O