CMT2157AW
Rev 0.8 | Page 12/31
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5. Functional Descriptions
Modulator
LDOs
VDD
GND
CLK
K0/DATA
XTAL
RFO
Loop
Filter
PFD/CP
Frac-N DIV
Encoder
Ramp-control
Interface & Control Logics
EEPROM
POR
PA
VCO
XOSC
Bandgap
LED Driver
LED
K[7:1]
K0
Figure 11. CMT2157AW Functional Block Diagram
5.1 Overview
The CMT2157AW is a true single-chip, highly flexible, high performance, OOK RF transmitter with embedded data encoder
ideal for 240 to 960 MHz wireless applications. It is part of the CMOSTEK NextGenRF
TM
family, which includes a complete line
of transmitters, receivers and transceivers. The device integrates a data encoder that is not only compatible with the most
common used encoding format of 1527 and 2262, but also a more efficient, flexible and powerful format of 1920 designed by
CMOSTEK. Up to 7 configurable push buttons are supported in multiple button modes. The device is optimized for the low
system cost, low power consumption, battery powered application with its highly integrated and low power design.
The functional block diagram of the CMT2157AW is shown in figure above. The CMT2157AW is based on direct synthesis of
the RF frequency by means of a fully integrated low-noise fractional-N frequency synthesizer. It uses a 1-pin crystal oscillator
circuit with the required crystal load capacitance integrated on-chip to minimize the number of external components. Every
analog block is calibrated on each Power-on Reset (POR) to an internal reference voltage source. The calibration can help the
chip to finely work under different temperatures and supply voltages. The transmission is triggered by pressing the push
button(s). The data is modulated and sent out by a highly efficient PA which output power can be configured from -10 to +13
dBm in 1 dB step size. RF Frequency, PA output power and other product features can be programmed into the embedded
EEPROM by the RFPDK and USB Programmer.
This saves the cost and simplifies the product development and
manufacturing effort. Alternatively, in stock product of 868.35 MHz is available for immediate demands with no need of
EEPROM programming. The CMT2157AW operates from 1.8 to 3.6 V so that it can finely work with most batteries to their
useful power limits. It only consumes 26.7 mA when transm10 dBm FSK signal at 868.35 MHz under 3.3 V supply
voltage.
5.2 Modulation, Frequency, Deviation and Symbol Rate
The CMT2157AW supports GFSK/FSK modulation with the symbol rate up to 100 ksps, as well as OOK modulation with the
symbol rate up to 40 ksps. The supported deviation of the (G)FSK modulation ranges from 1 to 200 kHz. It continuously covers
the frequency range from 240 to 960 MHz, including the license free ISM frequency band around 315 MHz, 433.92 MHz,
868.35 MHz and 915 MHz. The device contains a high spectrum purity low power fractional-N frequency synthesizer with
output frequency resolution better than 198 Hz when the frequency is less than 480 MHz, and is about 397 Hz when the
frequency is larger than 480 MHz. See Table 9 for the modulation, frequency, deviation and symbol rate specifications.
