EVB7122
27 to 930MHz Transceiver
Evaluation Board Description
1
1.1
Theory of Operation
General
The main building block of the transceiver is a programmable PLL frequency synthesizer that is based on an
integer-N topology. The PLL is used for generating the carrier frequency during transmission and for
generating the LO signal during reception. The carrier frequency can be FSK-modulated by pulling the
crystal and ASK-modulated by on/off keying of the power amplifier. The receiver is based on the principle of
a single conversion superhet. Therefore the VCO frequency has to be changed between transmit and
receive mode. In receive mode, the preferred LO injection type is low-side injection.
The TH7122 transceiver IC consists of the following building blocks:
"
"
"
"
"
"
"
Low-noise amplifier (LNA) for high-sensitivity
RF signal reception with switchable gain
Mixer (MIX) for RF-to-IF down-conversion
IF amplifier (IFA) to amplify and limit the IF
signal and for RSSI generation
Phase-coincidence demodulator with external
ceramic discriminator (FSK Demodulator)
Operational amplifier (OA1), connected to
demodulator output
Operational amplifier (OA2), for geral use
Peak detector (PKDET) for ASK detection
"
"
"
"
"
"
"
"
Control logic with 3wire bus serial control
interface (SCI)
Reference oscillator (RO) with external crystal
Reference divider (R counter)
Programmable divider (N/A counter)
Phase-frequency detector (PFD)
Charge pump (CP)
Voltage controlled oscillator (VCO) with internal
varactor
Power amplifier (PA) with adjustable output
power
1.2
Technical Data Overview
!
Sensitivity: -107 dBm at ASK with 180 kHz
IF filter BW
!
Max. data rate with crystal pulling: 20 kbps NRZ
!
Max. data rate with direct VCO modulation:
115 kbps NRZ
!
Max. input level: -10 dBm at FSK
and -20 dBm at ASK
!
Input frequency acceptance:
±
10 to
±
150 kHz
(depending on FSK deviation)
!
FM/FSK deviation range:
±2.5
to
±80
kHz
!
Analog modulation frequency: max. 10 kHz
!
Crystal reference frequency: 3 MHz to 12 MHz
!
External reference frequency: 1 MHz to 16 MHz
!
Frequency range: 300 MHz to 930 MHz in
programmable user mode
!
Extended frequency range with external VCO
varactor diode: 27 MHz to 930 MHz
!
315 MHz, 433 MHz, 868 MHz or 915 MHz fixed-
frequency settings in stand-alone mode
!
Power supply range: 2.2 V to 5.5 V
!
Temperature range: -40 °C to +85 °C
!
Standby current: 50 nA
!
Operating current in receive: 6.5 mA (low gain)
!
Operating current in transmit: 12 mA (at -2 dBm)
!
Adjustable RF power range: -20 dBm to
+10dBm
!
Sensitivity: -105 dBm at FSK with 180 kHz
IF filter BW
1.3
Note on ASK Operation
Optimum ASK performance can be achieved by using an 8-MHz crystal for operation at 315 MHz, 434 MHz
and 915 MHz. For details please refer to the software settings shown in sections 4.2 and 4.3. FSK operation
is the preferred choice for applications in the European 868MHz band.
For more detailed information, please refer to the latest TH7122 data sheet revision
39012 07122 02
Rev. 005
Page 3 of 24
EVB Description
June/07
MELEXIS [ Melexis Microelectronic Systems ]
