SI4322-A1-FT Silicon Laboratories Inc, SI4322-A1-FT Datasheet - Page 11

• Manufacturer Part Number: SI4322-A1-FT
• Description: IC RCVR FSK 915MHZ 3.8V 16-TSSOP
• Manufacturer: Silicon Laboratories Inc
• Type: FSK Receiverr

Specifications of SI4322-A1-FT

• Package / Case: 16-TSSOP
• Frequency: 868MHz, 915MHz
• Sensitivity: -104dBm
• Data Rate - Maximum: 256 kbps
• Modulation Or Protocol: FSK
• Applications: Remote Control, RKE, Security Systems
• Current - Receiving: 14mA
• Data Interface: PCB, Surface Mount
• Antenna Connector: PCB, Surface Mount
• Features: RSSI Equipped
• Voltage - Supply: 2.2 V ~ 3.8 V
• Operating Frequency: 915 MHz
• Operating Supply Voltage: 2.5 V, 3.3 V
• Maximum Operating Temperature: + 85 C
• Minimum Operating Temperature: - 40 C
• Mounting Style: SMD/SMT
• Supply Current: 12 mA
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Operating Temperature: -
• Memory Size: -
• Lead Free Status / Rohs Status: Supplier Unconfirmed
• Other names: 336-1628-5

Si4322
4. Functional Description
The Si4322 FSK receiver is the counterpart of Silicon Labs’ Si4022 FSK transmitter. It covers the unlicensed
frequency bands at 433, 868 and 915 MHz. The device facilitates compliance with FCC and ETSI requirements.
The receiver employs zero-IF approach with I/Q demodulation, allowing the use of a minimal number of external
components in a typical application. The Si4322 consists of a fully integrated multi-band PLL synthesizer, an LNA
with switchable gain, I/Q down converter mixers, baseband filters and amplifiers, and an I/Q demodulator followed
by a data filter.
4.1. PLL
The programmable PLL synthesizer determines the operating frequency, while preserving accuracy based on the
on-chip crystal-controlled reference oscillator. The PLL’s high resolution allows for the use of multiple channels in
any of the bands.
4.2. LNA
The LNA has 250  input impedance, which suits to the recommended antennas. (See Application Notes available
from www.silabs.com.)
If the RF input of the chip is connected to 50  devices, an external matching circuit is required to provide the
correct matching and to minimize the noise figure of the receiver.
The LNA gain can be selected (0, –6, –12, –18 dB relative to the highest gain) according to RF signal strength.
This is useful in an environment with strong interferers.
4.3. Baseband Filters
The receiver bandwidth is selectable by programming the bandwidth (BW) of the baseband filters. An appropriate
bandwidth can be selected to accommodate various FSK deviation, data rate, and crystal tolerance requirements.
th
The filter structure is a 7
order Butterworth low-pass with 40 dB suppression at 2 x BW frequency. Offset
cancellation is accomplished by using a high-pass filter with a cut-off frequency below 15 kHz.
Figure 1. Full Baseband Amplifier Transfer Function, BW = 135 kHz
4.4. Data Filtering and Clock Recovery
The output data filtering can be completed by an external capacitor or by using digital filtering according to the final
application.
Analog operation: The filter is an RC type low-pass filter followed by a Schmitt-trigger (St). The resistor (10k) and
the Schmitt-trigger (St) are integrated on the chip. The filter capacitor should be connected externally, its value
should be chosen according to the actual bit rate. In this mode, the receiver can handle up to 256 kbps data rate.
When the analog filter is selected, the FIFO cannot be used and clock is not provided for the demodulated data.
Rev. 1.2
11