PLUTO
PIN DESCRIPTION (continued)
No
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Pin Name
RXQP
RXQM
SUB
RXIP
RXIM
VDD
GND
VREF<0>
AD<0>
AD<1>
AD<2>
AD<3>
Vtest
EnTest
FC_Q
FC_I
BAL
VDD
GND
TXIP
TXIM
SUB
TXQP
TXQM
FMTX
VREF<1>
Type
Input
Input
Ground
Input
Input
Power
Ground
Input/Output
Input
Input
Input
Input
Output
Output
Output
Output
Output
Power
Ground
Output
Output
Ground
Output
Output
Output
Input/Output
A/D
Analog
Analog
Analog
Analog
Description
Receive Q Channel Input (+ve)
Receive Q Channel Input (-ve)
Substrate - Ground
Receive Q channel input (+ve)
Receive Q channel Input (-ve)
Power Supply
Ground
CDMA Receive Circuit Voltage Reference De-Coupling
AUX ADC Input
AUX ADC Input
AUX ADC Input
AUX ADC Input
RX Filter tuning tone output - pulled low when inactive
RX Filter tuning mode control output - pulled low when inactive
RX Filter Q channel FC control
RX Filter channel FC control
RX Filter Gain Balance Control
Power Supply
Ground
Transmit Circuit channel Complementary Output (+ve)
Transmit Circuit I channel Complementary Output (-ve)
Substrate - Ground
Transmit Circuit Q channel Complementary Output (+ve)
Transmit Circuit Q channel Complementary Output (-ve)
Transmit Circuit FM output
Transmit Circuit Voltage Reference De-coupling
Analog
Analog
Analog
Analog
Analog
Digital
Digital
Analog
Analog
Analog
Analog
Analog
Analog
Analog
Analog
Analog
FUNCTIONAL DESCRIPTION
Baseband TX interface circuit
The Pluto baseband transmit circuit acts as an interface
between the baseband signal processor and the RF/IF sections
in a CDMA/AMPS compatible mobile telephone.
The TX circuit has two modes of operation :
CDMA mode, transmit data that has previously been encoded
by the baseband digital signal processor is converted to
equivalent analog signals by matched digital-to-analog
converters, these signals are then filtered to remove the image
of the sample clock that would otherwise be present at the
output before being output to the I and Q modulator as
differential signals.
FM mode, transmit data is treated in much the same way as
in CDMA mode except that only one DAC is used and (because
of the much lower bandwidth of AMPS signals) a different
reconstruction filter is used before the analog fm signal is output
to the mixer as a single ended signal.
CDMA Transmit Signal Path
CDMA TX DACs
In CDMA mode two matched 8-bit DACs are used to
generate the in-phase and quadrature signals, the input
data for the DACs is obtained by multiplexing over an 8-bit
parallel input port (TXD<7:0>). The transmit data rate is
twice as fast as the differential transmit clock (TXCLK).
Incoming data that is valid during the rising edge of the
transmit clock is loaded into in In-Phase DAC & incoming
data that is valid on the falling edge of the transmit clock is
loaded into the Quadrature DAC - I and Q values must be
modified in the digital baseband chip to account for the half-
cycle delay between them.
CDMA Analog Reconstruction Filters
The frequency spectrum at the output of the transmit
DACs contains unwanted frequency components.
Reconstruction filters are used to smooth the DAC output
signals, providing continuous time output signals at the I and
Q output pins thereby removing these undesirable signals.
The low pass filters used are 5th order Butterworth,
continuous time filters with a nominal cut-off frequency of 1.2
MHz. These filters are designed to have a linear phase
response in the pass band. On-chip reconstruction filters
minimise the phase and amplitude mismatch between I and
Q channels.
3
MITEL [ MITEL NETWORKS CORPORATION ]
