AD6652

The AD6652 is a mixed-signal IF to baseband receiver consisting of dual 12-bit 65 MSPS ADCs and a wideband multimode digital downconverter (DDC). The AD6652 is designed to support communications applications where low cost, small size, and versatility are desired. The AD6652 is also suitable for other applications in imaging, medical ultrasound, instrumentation, and test equipment. 

The dual ADC core AD6652 features a multistage differential pipelined architecture with integrated output error correction logic. Both ADCs feature wide bandwidth differential sample-and-hold analog input amplifiers supporting a variety of user-selectable input ranges. An integrated voltage reference eases design considerations. A duty cycle stabilizer is provided to compensate for variations in the ADC clock duty cycle, allowing the converters to maintain excellent performance.  

ADC data outputs of AD6652 are internally connected directly to the receiver's digital downconverter (DDC) input matrix, simplifying layout and reducing interconnection parasitics. Overrange bits are provided for each ADC channel to alert the user to ADC clipping. Level indicator bits are also provided for each DDC input port that can be used for external digital VGA control.

The digital receiver AD6652 has four reconfigurable channels and provides extraordinary processing flexibility. The receiver input matrix routes the ADC data to individual channels, or to all four receive processing channels. Each receive channel has five cascaded signal processing stages: a 32-bit frequency translator (numerically controlled oscillator (NCO)), two fixed-coefficient decimating filters (CIC), a programmable RAM coefficient decimating FIR filter (RCF), and an interpolating half-band filter/AGC stage. Following the CIC filters, one, several, or all channels can be configured to use one, several, or all the RCF filters. This permits the processing power of four 160-tap RCF FIR filters to be combined or used individually.

After FIR filtering, data of AD6652 can be routed directly to the two external 16-bit output ports. Alternatively, data can be routed through two additional half-band interpolation stages, where up to four channels can be combined (interleaved), interpolated, and processed by an automatic gain control (AGC) circuit with 96 dB range. The outputs from the two AGC stages are also routed directly to the two external 16-bit output ports. Each output port has a 16-bit parallel output and an 8-bit link port to permit seamless data interface with DSP devices such as the TS-101 TigerSHARC® DSP. A multiplexer for each port selects one of six data sources to appear on the device outputs pins.

The AD6652 is part of the Analog Devices SoftCell® multimode and multicarrier transceiver chipset. The SoftCell receiver digitizes a wide spectrum of IF frequencies and then downconverts the desired signals to baseband using individual channel NCOs. The AD6652 provides user-configurable digital filters for removal of undesired baseband components, and the data is then passed on to an external DSP, where demodulation and other signal processing tasks are performed to complete the information retrieval process. Each receive channel is independently configurable to provide simultaneous reception of the carrier to which it is tuned. This IF sampling architecture greatly reduces component cost and complexity compared with traditional analog techniques or less integrated digital methods. 

High dynamic range decimation filters AD6652 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 occupies less bandwidth than the input signal, this rejection of out-of-band noise is referred to as processing gain. By using large decimation factors, this processing gain can improve the SNR of the ADC by 20 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.

Flexible power-down options of AD6652 allow significant power savings, when desired.