2.0 Functional Description
The TXC101 is a low power, frequency agile, multi-channel OOK/FSK transmitter for use in the 315, 433,
868, and 916 MHz bands. All RF transmit functions are completely integrated requiring only a single
10MHz crystal as a reference source. The TXC101 has two modes of operation: EEPROM mode and
Processor mode. EEPROM mode is fully compatible with any standard SPI interface EEPROM.
Functions include:
•
PLL synthesizer
•
Power Amp
•
Crystal oscillator
•
Sleep Timer
•
OOK/FSK Modulation
•
4 Key/Switch Functions
The TXC101 is ideal for Frequency Hopping Spread Spectrum (FHSS) applications requiring frequency
agility to meet FCC and ETSI requirements. Use of a low-cost microcontroller or SPI compatible
EEPROM is all that is needed to create a complete transmitter. The TXC101 also incorporates different
sleep modes to reduce overall current consumption and extend transmitter battery life. It is ideal for
applications operating from typical lithium coin cells.
2.1 TXC101 Processor Mode and Application Circuit
Figure 1. Typical Processor Mode Application Circuit for 50 Ohm Load
The TXC101 may be used with a typical low-cost microcontroller. All internal functions are accessible
through the SPI interface. Figure 1 shows a typical connection for using a microcontroller to control the
TXC101 functions.
RF Transmitter Matching
The RF pins are high impedance and differential. The optimum differential load for the RF port at a given
frequency band is shown in Table 1.
TABLE 1.
Admittance [S] Impedance [Ohm] Lantenna (nH)
9.4e-4 – j4.5e-3
43 + j214
112
315 MHz
21 + j157
59
433 MHz
8.4e-4 – j6.25e-3
7.9 + j83
15.3
868 MHz
1.15e-3 – j1.2e-2
7.6 + j79
13.9
916 MHz
1.2e-3 – j1.25e-2
5
RFM [ RF MONOLITHICS, INC ]
