Wideband, Multichannel Front End Tackles Direct C-Band RF Sampling

We’re so accustomed to ICs in the $1 price range that it’s easy to presume something is wrong when you see one priced above $1000. Still, some ICs have the features, functions, and performance specifications whereby their vendor feels that they can command that amount.

The latest such pair is the highly integrated quad-channel AFE7444 and similar dual-channel AFE7422 RF-sampling transceivers from Texas Instruments (Fig. 1). These devices target wideband systems including multiantenna, direct-sampling radar, and 5G applications, with what TI maintains is industry’s widest frequency range and smallest footprint. The level of integration allows for sampling of frequencies to 6 GHz (the most-used portion of the C-band, formally defined at 4 to 8 GHz) without the need for additional frequency-conversion stages, thus eliminating local oscillators, mixers, amplifiers, and filters.

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1. The highly integrated quad-channel AFE7444 from Texas Instruments enables direct-digital sampling into the 6-GHz band; the AFE7422 is a two-channel version.

The quad-channel IC integrates 14-bit digital-to-analog converters (DACs) and 14-bit analog-to-digital converters (ADCs) that, along with its high instantaneous bandwidth, enables sampling to 9 Gsamples/s per DAC and up to 3 Gsamples/s per ADC. The AFE7444 can receive and transmit up to 800-MHz bandwidth from each of four antennas, while the AFE7422 receives and transmits 1.2 GHz from each of two antennas. Their 8-lane (8 TX + 8 RX) JESD204B interface (subclass-1 compliant) operates at up to 15 Gb/s.

Transmit-side DAC features and performance: The DAC signal paths support interpolation and digital up-conversion options to deliver the wide bandwidth; their differential output path includes a per-channel digital step attenuator (DSA) for optimal tuning of output power. Other DAC features include dual digital upconverters (DUCs), 32-bit NCOs, 8× to 36× interpolation ratio, sin(x)/x correction and configurable delay, and power-amplifier protection (PAP).

Receive-side ADC features and performance: Each ADC path includes dual DSAs to extend dynamic range, along with RF and digital power detectors. ADC noise spectral density (NSD) is −151 dBFS/Hz; while dynamic performance (−3 dBFS at f_IN of 2.6 GHz) includes SNR of 55 dBFS; SFDR of 73 dBc (HD2 and HD3); and worst-spur SFDR of 91 dBc. Flexible decimation options allow for optimization of data bandwidth.

Clocks are critical parts of the transmit and receive signal chain. These ICs include an internal phase-locked loop (PLL) and voltage-controlled oscillator (VCO) with bypass option, along with clock output up to 3 GHz with clock divider. Fast frequency hopping at under 1 μs makes this pair a good fit for the demands of the target applications.

Size and power: An IC such as this one is also characterized by its dissipation and footprint. DAC- and ADC-path dissipation are just under 2 W each at 9 and 3 Gsamples/s, respectively. The devices are housed in 400-contact, 0.8-mm-pitch, 17- × 17- × 2.65-mm flip-chip BGA packages, which TI says will reduce required PCB space by 75% compared to using discrete RF-sampling data converters. Also important, the small size of these ICs makes it possible to place them close to system antennas for improved beamforming in high-frequency/high-density arrays.

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2. Setting up and exercising an IC such as the AFE7444 calls for great care and attention to RF detail. The AFE7444EM evaluation board is an RF-sampling transceiver platform that can be configured to support up to four transmit and four receive channels simultaneously.

Pricing and support: The AFE7444 quad-channel, wideband RF-sampling transceiver is priced at $1,749.90, while the dual-channel AFE7422 sibling goes for $1,249.90, in 100-piece lots. To assist in evaluating these transceivers, TI offers quad/dual-channel evaluation modules, the AFE7444 and AFE7422, at $2,499 and $1,999 respectively (Fig. 2).

Along with other application notes for these transceivers, TIDA-010131 “Multichannel RF transceiver clocking reference design for radars and wireless 5G testers” demonstrates development of the multichannel clocks, which are critical to achieving specified system performance. There’s also a video series: “Getting started with the AFE7444 and AFE7422.”