6.9 Transmitter – External Power Amplifier and Subcarrier Detector
The TRF7970A can be used in conjunction with an external TX power amplifier or external subcarrier detector for the receiver path. In this case, certain registers must be programmed as shown here:
- Bit B6 of the Regulator and I/O Control register (0x0B) must be set to 1. This setting has two functions: first, to provide a modulated signal for the transmitter if needed, and second, to configure the TRF7970A receiver inputs for an external demodulated subcarrier input.
- Bit B3 of the Modulation and SYS_CLK Control register (0x09) must be set to 1 (see Section 6.15.3.2.8). This function configures the ASK/OOK pin for either a digital or analog output (B3 = 0 enables a digital output, B3 = 1 enables an analog output). The design of an external power amplifier requires detailed RF knowledge. There are also readily designed and certified high-power HF reader modules on the market.