Two-chip IF receiver solution from Analog Devices

The AD8376 and AD6655 comprise the first two-chip dual-channel IF receiver optimized to handle both the main and diversity receive paths simultaneously. The combination of best-in-class performance, power consumption, size and cost is ideally suited to meet the wider bandwidth and multi-carrier signal processing demands of today’s wireless infrastructure equipment, while supporting emerging 3G and 2.5G mobile phone communications standards such as CDMA2000, UMTS and TD-SCDMA, as well as WiMAX.

As the industry migrates from voice-centric services and embraces feature-rich, multimedia content, wireless infrastructure designers need devices that support the higher data bandwidths within the next-generation of mobile communications platforms, said Peter Real, product line director, RF and Networking Components, Analog Devices. To help address this need, ADI developed the industry’s highest linearity digital VGA and the fastest IF diversity receiver, which when combined, not only reduce component count, but bring complex multi-carrier wideband digital receivers into mainstream production.

The AD8376 is the first digitally-controlled VGA that enables 1dB gain-step resolution at the highest IFs. The device offers the industry’s best linearity of OIP3 50 dBm at 140 MHZ. This level of performance and step resolution simplifies receiver automatic gain control (AGC), and enables wideband multi-carrier radio platforms. A fine-step AGC loop allows the designer to maximize the ADC’s dynamic range, which is critical when handling either 3G or WiMAX multi-carrier wideband input signals.

The AD8376 dual-channel VGA provides precise fine-gain-step adjustment for digital radio receivers. The device features a bandwidth of 600 MHz, supporting high IF sampling receiver architectures within cellular and broadband WiMAX receivers. An independent 5-pin digital interface allows the user to take advantage of a 24dB gain range and 1dB gain-step resolution. The AD8376 is designed to replace discrete attenuator and IF amplifiers, offering considerable board and package density savings. With 50dBm output IP3 on 130mA of quiescent current on a +5volt supply, current consumption is also significantly reduced.

The AD6655 integrates many of the functions required for diversity receive path in a single device, including an ultra-low-latency peak detector and an rms signal power monitor that can be used in conjunction with the AD8376 and logic to form a flexible AGC. In addition, the AD6655 includes the industry’s fastest 14-bit ADC (analog-to-digital converter), at 150 MSPS (million samples per second), followed by a DDC (digital down converter). The DDC functionality includes a 32-bit NCO (numerically controlled oscillator), a decimating half-band filter and an output FIR (finite-impulse response) filter. Together, these provide an effective bandpass filtering function and reduce the output rate, which yields an SNR (signal-to-noise ratio) of 75 dB at 70 MHz, an improvement of 2.5 dB over the typical ADC. By integrating the DDC with the ADC, designers realize a significant reduction in board space while eliminating the high-speed interconnect problems usually found on system boards when the devices are implemented separately.

The AD6655 is offered in both 12- (AD6653) and 14-bit resolutions with sample rates of 80 MSPS, 105 MSPS, 125 MSPS and 150 MSPS. For applications that require only the dual-ADC function without the DDC, the recently-announced AD9640 is pin compatible and includes signal monitor, level detection, and 1-to-8 clock divider.

The AD8376 dual-channel digitally-controlled VGA is sampling now with full production scheduled for June 2007. The AD8376 is priced at $6.25 per unit in 1,000-piece quantities and is housed in a 32-lead LFCSP (lead-frame chip-scale package). A single-channel version, the AD8375, is sampling now with full production also scheduled for June 2007. The AD8375 is priced at $4.25 per unit in 1,000-piece quantities and is housed in a 24-lead LFCSP.

The AD6653/5 IF diversity receivers are sampling now with full production scheduled for June 2007. The 12-bit version, the AD6653, is priced at $57.97 and the 14-bit at $97.50, both in 1,000-piece quantities. Both devices are available in a 9 mm x 9 mm 64-lead LFCSP.