Rainbow Electronics ATA5746 - Manual (Page 2)

2
4596A–RKE–05/06
ATA5745/ATA5746 [Preliminary]
1. General Description
The ATA5745/ATA5746 is a UHF ASK/FSK transparent receiver IC with low power consumption
supplied in a small QFN24 package (body 5 mm
× 5 mm, pitch 0.65 mm). ATA5745 is used in
the 433 MHz to 435 MHz band of operation, and ATA5746 in 313 MHz to 317 MHz. The IC com-
bines the functionality of remote keyless entry (RKE - typically low bit rate ASK) and tire
pressure monitoring (TPM - typically high bit rate FSK) into one receiver under the control of an
external microcontroller such as an ATmega48 (AVR
® ).
For improved image rejection and selectivity, the IF frequency is fixed to 440 kHz. The IF block
uses an 8th-order band pass yielding a receive bandwidth of 420 kHz. This enables the use of
the receiver in both SAW- and PLL-based transmitter systems utilizing various types of data-bit
encoding such as pulse width modulation, Manchester modulation, variable pulse modulation,
pulse position modulation, and NRZ. Prevailing encryption protocols such as Keeloq
® are easily
supported due to the receiver’s ability to hold the current data slicer threshold for up to 52 ms
when incoming RF telegrams contain a blanking interval. This feature eliminates erroneous
noise from appearing on the demodulated data output pin, and simplifies software decoding
algorithms. The decoding of the data stream must be carried out by a connected microcontroller
device. Because of the highly integrated design, the only required RF components are for the
purpose of receiver antenna matching.
ATA5745 and ATA5746 support Manchester bit rates of 1 Kbit/s to 10 Kbits/s in ASK and 1 Kbit/s
to 20 Kbits/s in FSK mode. The four discrete bit rate passbands are selectable and cover
1.0 Kbit/s to 2.5 Kbits/s, 2.0 Kbits/s to 5.0 Kbits/s, 4.0 Kbits/s to 10.0 Kbits/s, and 8.0 Kbits/s to
10.0 Kbits/s or 20.0 Kbits/s (for ASK or FSK, respectively). The receiver contains an RSSI output
to provide an indication of received signal strength and a SENSE input to allow the customer to
select a threshold below which the DATA signal is gated off. ASK/FSK and bit rate ranges are
selected by the connected microcontroller device via pins ASK_NFSK, BR0, and BR1.
Figure 1-1. System Block Diagram
(LNA, Mixer,
VCO, PLL,
IF Filter,
RSSI Amp.,
Demodulator)
RF Receiver
ATA5745/ATA5746
Antenna
XTO
Microcontroller
Microcontroller
Interface
4 ... 8
Power
Supply
Digital Control
Logic