Table of Contents
Advertisement
Technical Description
TX Filtering
The reduction of TX spurious emissions and TX noise in the RX band is achieved
with two filters. The first is a bandpass SAW filter. The second filter is the TX
branch of the duplexer filter. The response is predominately band-pass with a notch
in the RX band to protect the receiver from TX noise power. High frequency attenu-
ation provides reduction in the level of TX harmonics.
Protection against Electro-Static Discharge (ESD) is also provided by the high-pass
element of the duplexer TX branch.
MALIN
MALIN, is an integrated RF circuit for FDMA cellular telephones. The circuit is
designed for a radio architecture using one synthesizer for both RX and TX parts.
The transmitter portion consists of a TX-IF VCO and a TX-mixer. The base-band
signal modulates the TX-IF via an external tank circuit which is then up-converted
to the TX frequency by the TX-mixer. A programmable prescaler is included for use
in the main synthesizer loop, and power down control is provided for current saving.
TX-IF VCO
The TX-IF is generated by an internal oscillator of MALIN. Tuning is performed by
an external tank circuit where the center frequency is controlled by the auxiliary
synthesizer using a varactor diode. The TX-IF signal is also buffered and sent to the
auxiliary synthesizer to maintain a constant 90 MHz TX-IF frequency.
TX Mixer
The TX mixer multiplies the TX-IF signal with the first LO signal from the main
VCO to create the desired output signal. The mixer is designed to have a low noise
floor in order not to affect the receiver performance. The output is differential and
an LC network is used to align the signals to make them combine constructively.
TX Modulation
The modulation of the transmitter occurs in the TX-IF VCO tank circuit. The base-
band signal coming from the audio IC ANTON is filtered and used to shift the reso-
nant frequency of the external tank circuit by the varying capacitance of the varactor
diode.
TX-IF Frequency Control
The center frequency of the TX-IF VCO is controlled by the auxiliary synthesizer
located in BERTINDY. A portion of the TX-IF signal is buffered and sent to the TX
oscillator outputs. This signal is used to lock the TX-IF in the Auxiliary PLL.
Programmable Prescaler
MALIN also includes a prescaler for use in the main synthesizer loop. The divider
has separate Vcc and ground connections to provide good isolation from the TXPA
outputs.
19
Advertisement
Chapters
Table of Contents
