SI4021 Datasheet, PDF (1/35 Pages) Silicon Laboratories – Automatic antenna tuning circuit

Si4021 Universal ISM
Band FSK Transmitter
DESCRIPTION
Silicon Labs’ Si4021 is a single chip, low power, multi-channel FSK
transmitter designed for use in applications requiring FCC or ETSI
conformance for unlicensed use in the 433, 868, and 915 MHz bands.
Used in conjunction with Si4020, Silicon Labs’ FSK receiver, the Si4021
transmitter features EZRadioTM technology, which produces a flexible, low
cost, and highly integrated solution that does not require production
alignments. All required RF functions are integrated. Only an external
crystal and bypass filtering are needed for operation. The Si4021 builds on
the features presented by the Si4020 by offering a higher output power
and an improved phase noise characteristic. The Si4021 shares the same
pinout and control command set as the Si4020. The Si4021 offers all of
the frequencies as the Si4020, with the exception of the 315 MHz band.
The Si4021 features a completely integrated PLL for easy RF design, and
its rapid settling time allows for fast frequency hopping, bypassing
multipath fading and interference to achieve robust wireless links. In
addition, highly stable and accurate FSK modulation is accomplished by
direct closed-loop modulation with bit rates up to 115.2 kbps. The PLL’s
high resolution allows the use of multiple channels in any of the bands.
The integrated power amplifier of the transmitter has an open-collector
differential output that directly drive a loop antenna with programmable
output level. No additional matching network is required. An automatic
antenna tuning circuit is built in to avoid costly trimming procedures and
de-tuning due to the “hand effect”.
For low-power applications, the device supports automatic activation from
sleep mode. Active mode can be initiated by several wake-up events (on-
chip timer timeout, low supply voltage detection, or activation of any of the
four push-button inputs).
The Si4021’s on-chip digital interface supports both a microcontroller
mode and an EEPROM mode. The latter allows complete data transmitter
operation without a microcontroller (both control commands and data are
read from the EEPROM). Any wake-up event can start a transmission of the
corresponding data stored in the EEPROM.
FUNCTIONAL BLOCK DIAGRAM
XTL
MOD
VDD
VSS
CRYSTAL
OSCILLATOR
LOW
BATTERY
DETECT
WAKE-UP
TIMER
REFERENCE
SYNTHESIZER
LOAD CAP
LOW BAT
TRESHOLD
CLOCK
FREQUENCY
LEVEL
OOK
CONTROLLER
TIMEOUT
PERIOD
RFP
RFN
nIRQ/nLBD
CLK/SDO
SDI
SCK
nSEL
FSK
PB1 PB2 PB3 PB4
Si4021
PIN ASSIGNMENT
SDI 1
SCK
2
nSEL ³
PB1 ⁴
PB2 ⁵
PB3 ⁶
PB4 ⁷
CLK ⁸
16 FSK
SDI 1
15
VDD
SCK ²
14
nIRQ
nSEL 3
13 RFP
PB1 4
12 RFN
PB2 5
11 MOD
PB3 6
10 VSS
PB4 7
9
XTL
SDO 8
16 FSK
15 _VDD
14 nLBD
13 RFP
12 RFN
11 MOD
10 VSS
9
XTL
Microcontroller Mode
EEPROM Mode
This document refers to Si4021-IC Rev A1.
See www.silabs.com/integration for any applicable
errata. See back page for ordering information.
FEATURES
 Fully integrated (low BOM, easy design-in)
 No alignment required in production
 Fast settling, programmable, high-resolution PLL
 Fast frequency hopping capability
 Stable and accurate FSK modulation with programmable
deviation
 Programmable PLL loop bandwidth
 Direct loop antenna drive
 Automatic antenna tuning circuit
 Programmable output power level
 Alternative OOK support
 EEPROM mode supported
 SPI bus for applications with microcontroller
 Clock output for microcontroller
 Integrated programmable crystal load capacitor
 Multiple event handling options for wake-up activation
 Push-button event handling with switch de-bounce
 Wake-up timer
 Low battery detection
 2.2 to 5.4 V supply voltage
 Low power consumption
 Low standby current (0.3 µA)
 Compact 16-pin TSSOP package
 Transmit bit synchronization
TYPICAL APPLICATIONS
 Remote control
 Home security and alarm
 Wireless keyboard/mouse and other PC peripherals
 Toy control
 Remote keyless entry
 Tire pressure monitoring
 Telemetry
 Personal/patient data logging
 Remote automatic meter reading
Si4021-DS Rev 2.3r 0408
1
www.silabs.com/integration