Table of Contents
Advertisement
OVERVIEW: iDEN Digital Modulation
Technology
1
.7
iDEN Receiver Path
T
he receiver is a direct conversion receiver. It operates in the commercial portion of the
la
nd-mobile receiver band (851-870MHz and 935-940). It also operates in the ISM band
(9
02-928MHz) using the MOTOTALK protocol.
Figure 10 iDEN Receiver Path
The receiver takes an incoming RF signal, down-converts it to baseband where it is amplified,
filtered, digitized and then provided to
the DSP MODEM. The receiver has automatic gain control
(AGC) to maintain linearity over a wide range of incoming signals.
The AGC circuitry also
prevents clippin
1.7.1 Rx Front End (RX Path)
The Rx Front End contains the two SP3T RF switches, the passive SAW filters, along with the
active LNA and the balun. The antenna switch routes the received signal from the antenna pin
input to the receiver front end. During transmit mode, this switch disconnects the receiver path and
connects the antenna to the transmit path.
The pre-selector SAW
filters protect the RF LNA from strong out-of band signals. There are two
filters in each SAW filters (800MHz and 900MHz for one SAW filter and ISM and GPS band for
the other SAW filter) that are appropriately selected by the SP3T RF switches, for the appropriate
band of operation. The LNA RF amplifier contains three major blocks, a 20dB step attenuator, a
LNA, and an AGC.
The low-noise amplifier provides the gain to achieve the necessary receiver system take over gain
and the AGC stage provides continuous atten
uation to avoid overload of the receiver backend. A
balun is used to facilitate the conversion of the single ended LNA output to a differential signal
that is necessary to feed the input block of the Sledgehammer IC.
1.7.2 Sledgehammer IC (RX Path)
The Sledgehammer IC contains the frequency synthesizers, down-conversion mixers,
baseband
a
mplification and filtering stages. The main function of the Sledgehammer IC is to translate the
RF input signal in to the two I and Q b
aseband differential signals. The signal path has a fixed
amount of gain and contains the DC offs
et correction circuitry. The IC contains basic analog
anti-aliasing filtering and supplies a digital control line directly to the LNA module.
6880401P26-O
31
Advertisement
Table of Contents
