AD9375 Device Architecture
The AD9371 is a highly integrated RF transceiver. It integrates all the RF, mixed-signal, and digital blocks necessary to provide transmit and receive functions in a single device. Programmability allows the two receiver channels and two transmitter channels to be used in TDD and FDD systems for 3G and 4G cellular standards.
The AD9371 employs a direct conversion transmitter architecture consisting of two identical and independently controlled channels that provide all the digital processing, mixed signal, and RF blocks necessary to implement a direct conversion system. Both channels share a common frequency synthesizer.
The digital data from the JESD204B lanes pass through a fully programmable 96-tap FIR filter with optional interpolation. The FIR output is sent to a series of conversion filters that provide additional filtering and data rate interpolation prior to reaching the DAC. Each DAC has an adjustable sample rate and is linear up to full scale.
When converted to baseband analog signals, the in-phase (I) and quadrature (Q) signals are filtered to remove sampling artifacts, and then the signals are fed to the upconversion mixers. At the mixer stage, the I and Q signals are recombined and modulated onto the carrier frequency for transmission to the output stage. Each transmit chain provides a wide attenuation adjustment range with fine granularity to help designers optimize SNR.
The AD9371 contains dual receiver channels. Each Rx channel is a direct conversion system that contains a programmable attenuator stage, followed by matched I and Q mixers that downconvert received signals to baseband for digitization.
To achieve gain control, a programmed gain index map is implemented. This gain map distributes attenuation among the various Rx blocks for optimal performance at each power level. In addition, support is available for both automatic and manual gain control modes.
The receiver includes Σ-Δ ADCs and adjustable sample rates that produce data streams from the received signals. The signals can be conditioned further by a series of decimation filters and a fully programmable 72-tap FIR filter with additional decimation settings. The sample rate of each digital filter block is adjustable by changing the decimation factors to produce the desired output data rate.