The integrated RF sampling transceiver supports fast frequency hopping, multi-band, and multi-mode operation

　　The latest direct radio frequency (RF) sampling transceivers—including Texas Instruments' AFE7444 and AFE7422 devices, supporting four and two antenna channels respectively—offer a range of powerful features that enable advanced system features such as multi-band and multi-mode operation, as well as frequency conversion and fast frequency hopping.

　　Integrated RF sampling transceivers support fast frequency hopping, multi-band, and multi-mode operations. From a system perspective, these functions are becoming increasingly popular, such as multifunctional arrays. Different subarrays of large phased array antennas can be configured to perform various functions according to specific conditions or task requirements; This includes radar, communications, or electronic warfare (EW) capabilities, as shown in Figure 1.

　　Integrated RF sampler transceivers support fast frequency hopping, multi-band and multi-mode operation. Multifunctional phased array systems Moreover, these systems often require rapid frequency hopping to gradually adjust to operating frequencies through repeated or arbitrary sequences, as shown in Figure 2. Executing this approach can avoid human interference, prevent signal detection, or facilitate the implementation of anti-electronic spoofing techniques (electronic spoofing: tampering with the electronic signature of radar reflected signals).

　　Figure 2

　　Integrated RF sampling transceivers support fast frequency hopping, multi-band, and multi-mode operation with frequency agility across multiple Nyquist regions. To further understand these features, let's first examine the functional modules of integrated RF sampling transceivers, as shown in Figure 3.

　　Integrated RF sampling transceivers support fast frequency hopping, multi-band and multi-mode operation AFE7444/AFE7422 Functional modules of RF sampling transceivers. When the receiver and transmitter are used together, these modules provide enhanced features in the following ways:

　　It operates across an extremely wide RF frequency range from several MHz up to 6 GHz, handling extremely broad non-instantaneous bandwidth, up to 1.5 GHz.

　　Digital signal processing modules support aggregation and deaggregation of multiple sub-bands or waveforms, each sub-band or waveform can be processed as an independent digital data stream on either the receiving or transmitting side.

　　Multi-band or multi-mode signal processing

　　Now let's consider use cases for handling multi-band or multi-mode signals by leveraging broadband sampling, synthesis, and digital processing capabilities. As shown in Figure 4.

　　Figure 4

　　The integrated RF sampling transceiver supports fast frequency hopping, multi-band, and multi-mode operations. Using AFE7422 and AFE7444 multiband transmission and reception configurations, this setup generates a multiband signal consisting of three different sub-bands, with a total bandwidth of 2.75 GHz. The receiver samples across the entire frequency band across multiple Nyquist zones, then feeds the sample data to a digital downconversion module (with multiple parallel stages). The method involves using independent digital control oscillators (NCOs) and digital mixers, selecting multiple sub-bands and converting them into baseband signals. Apply sampling, then reduce output sampling rate and suppress out-of-band loss based on the bandwidth of individual signals.

　　Conversely, on the transmitting side, each digital input stream is fed into multiple parallel digital upconversion stages, and upconversion converts the baseband signal to its corresponding target frequency. Then, the data is supersampled to the output sampling rate of the RF digital-to-analog converter (DAC), which is then synthesized into a merged wideband signal (ranging from 700 MHz to 3.45 GHz) through the RF DAC in the final stage.

　　Frequency conversion and frequency hopping

　　You can extend the previous case by selecting only a single band, using internal digital loopbacks, and then applying frequency shifts to the selected subband before retransmitting the signal. As shown in Figure 5.

　　Figure 5

　　The integrated RF sampling transceiver supports fast frequency hopping, multi-band, and multi-mode operations, using AFE7444/AFE7422 to achieve frequency conversion or frequency hopping. This setup captures the multi-band signals mentioned earlier. The digital down-conversion module selects an independent sub-tape, converts it into a baseband signal, and transmits it through a digital filter. Digital filters remove out-of-band loss, such as harmonics or mixer products. The in-chip digital loop-back path supports directly feeding digital output data from the digital receiver into the transmitter path without leaving the chip or connecting any additional processing devices.

　　By simply converting the filtered signal upward back to the initial received frequency, the on-chip digital repeater is built. To deploy a frequency hopping transmitter, the transmitter's NCO must be programmed to output the required new frequency, and then the frequency shift signal is retransmitted. As shown in Figure 5, the yellow trace in the spectrum analyzer is shown and compared with the initially received multiband spectrum (green trace).

　　Figure 6

　　Integrated RF sampler transceivers support fast frequency hopping, multi-band, and multi-mode operation frequency transitions on oscillators so far. I have illustrated the basic concepts, and similar methods can be used to support other use cases, including:

　　Multi-band frequency conversion. Because multiple parallel digital down-inverter and up-converter modules are used, you can receive and deaggregate multiband signals into multiple independent sub-band signals, then apply independent frequency shifts to each sub-band signal, feed back to the transmitter path via the on-chip internal digital loop, and retransmit the sub-band signal after reaching a new frequency.

　　Fast frequency hopping. Because we can reprogram NCOs to obtain updated frequencies within milliseconds, or rotate multiple NCOs available on each signal path in ping-pong mode, we can receive and send frequency-agility signals in repeatable or arbitrary sequences. The conversion between these two frequencies is shown in Figure 6.

　　Ramp generation/direct digital synthesis mode. The built-in sine wave audio generator for each transmitter supports generating frequency ramps and FMCW (FMCW) commonly used in radar systems.

　　Simultaneous wideband scanning and narrowband observations. Since each receiver's front-end sampling stage can connect multiple digital processing stages, you can choose to configure a receive path for broadband mode. It outputs sampling data spanning the full frequency band of Nyquist and observes non-instantaneous bandwidths up to 1.5 GHz, thereby scanning for the presence of any signals. At the same time, you can configure a second path in the narrowband sampling mode to amplify and precisely analyze all signals detected in the wideband mode.