LEO satellite payload supporting D2D and IoT can benefit significantly from the ability to operate across multiple frequency bands simultaneously. In traditional discrete RF architectures, multi-band operation can require duplicating significant portions of the signal chain, including mixers, oscillators, and data converters. In contrast, the AFE8030’s direct RF-sampling architecture simplifies multi-band implementation by performing frequency conversion and band combination and separation digitally.

The AFE8030 incorporates dual digital up-converter (DUC) and digital down-converter (DDC) chains per transceiver channel, each operating independently with dedicated numerically controlled oscillators (NCOs), as shown in Figure 5-1 and Figure 5-2. A single AFE8030 can therefore simultaneously up-convert two transmit bands and down-convert two receive bands without the overhead of additional mixers and oscillators.

Consider simultaneous L- and S-band coverage as a typical example of a satellite D2D application. With a DAC sampling frequency of 6GSPS and a ADC sampling rate of 3GSPS, the AFE8030 can cover the L band and the lower half of the S band within the same Nyquist zone. The AFE8030 can be configured in dual-DUC and dual-DDC modes. With dual-DUC mode, two independent DUC chains can process the respective frequency bands and combine them into a single transmitter output. With dual-DDC mode, the single receiver can digitize both bands through one ADC, and the two independent DDC chains can separate the two frequency bands in the digital domain. Additionally, each of the AFE8030’s eight transmitter and eight receiver chains can be configured with independent NCO frequencies, providing additional flexibility for multi-band operation and spectrum allocation.

The relatively narrow bandwidths of D2D and IoT waveforms fit easily within the available bandwidth of each DUC and DDC chain, allowing flexible on the choice of center frequencies through digitally controlled NCO. Additionally, as each DUC and DDC chain have two independent NCOs, the AFE8030 enables fast switching between multiple center frequencies within each band.

Together, the AFE8030 allows simultaneous multi-band coverage using a single RF transceiver, with frequency conversion and band combination/separation maintained in the digital domain of the device. Compared to traditional architecture, this approach significantly reduces component count and hardware complexity. Figure 5-3 shows an example of the transmitter output spectrum, where the single transmitter chain of AFE8030 is sending out both L- and S-band signal simultaneously with the dual-DUC mode.

With all the advantages of dual-DUC and dual-DDC modes, simultaneous multi-band operation requires careful RF frequency planning and filtering. In the multi-band configuration, the DACs and ADCs process the combined spectrum spanning multiple bands, designers must do frequency planning wisely to avoid unwanted intermodulation components falling in-band, and design the filter placement carefully to provide sufficient rejection on out-of-band inter-band modulation components. On the receiver side, the digital decimation filters in AFE8030 can provide approximately 85dB or greater out-of-band rejection following digital band separation.

Another important consideration is system power efficiency. Although dual-DUC operation simplifies the transceiver architecture, a broadband power amplifier covering multiple bands can be less efficient than narrowband amplifiers optimized for individual bands. Designers must therefore evaluate the tradeoffs among RF integration, filtering complexity, power amplifier efficiency, and overall system power consumption based on the intended specific use cases.