AD6635

The AD6635 is a multimode, 8-channel, digital Receive Signal Processor (RSP) capable of processing up to four WCDMA channels. Each channel consists of four cascaded signal-processing elements: a frequency translator, two CIC decimating filters, and a programmable coefficient-decimating filter. Each input port has input level threshold detection circuitry for accommodating large dynamic ranges or situations where gain ranging converters are used. Quad 16-bit parallel output ports accommodate high data rate WBCDMA applications. On-chip interpolating half-band filters can also be used to further increase the output rate. In addition, each output port has a digital AGC for accommodating large dynamic ranges using smaller bit widths. The AGCs can maintain either signal level or clipping level, depending on their mode. Link port outputs are provided to enable glueless interfaces to Analog Devices' TigerSHARC DSP core.

The AD6635 is part of Analog Devices' SoftCell Multicarrier transceiver chipset designed for compatibility with Analog Devices' family of high sample rate IF sampling ADCs (AD9238/AD6645 12-bit and 14-bit). The SoftCell receiver comprises a digital receiver capable of digitizing an entire spectrum of carriers and digitally selecting the carrier of interest for tuning and channel selection. This architecture eliminates redundant radios in wireless base station applications.

High dynamic range decimation filters offer a wide range of decimation rates. The RAM-based architecture allows easy reconfiguration for multimode applications.

The decimating filters remove unwanted signals and noise from the channel of interest. When the channel of interest occupies less bandwidth than the input signal, this rejection of out-of-band noise is called "processing gain." By using large decimation factors, processing gain can improve the SNR of the ADC by 30 dB or more. In addition, the programmable RAM coefficient filter allows antialiasing, matched filtering, and static equalization functions to be combined in a single, cost-effective filter. Half-band interpolating filters at the output are used in various applications, especially in WCDMA or cdma2000 applications, to increase the output rate from 2* to 4* the chip rate. The AD6635 is equipped with four independent automatic gain control (AGC) loops for direct interface to a RAKE receiver.

The AD6635 is compatible with standard ADC converters, such as the AD664x, AD943x, AD923x, and the AD922x families of data converters. The AD6635 is also compatible with the AD6600 Diversity ADC, and hence can be designed into existing systems that use AD6600 ADCs.