AD8339:  DC to 50 MHz, Quad I/Q Demodulator and Phase Shifter

The AD8339 is a quad I/Q demodulator configured to be driven by a low noise preamplifier with differential outputs. It is optimized for the LNA in the AD8332/AD8334/AD8335 family of VGAs. The part consists of four identical I/Q demodulators with a 4× local oscillator (LO) input that divides this signal and generates the necessary 0° and 90° phases of the internal LO that drive the mixers. The four I/Q demodulators can be used independently of each other (assuming that a common LO is acceptable) because each has a separate RF input.

Continuous wave (CW) analog beamforming (ABF) and I/Q demodulation are combined in a single 40-lead ultracompact chip scale device, making the AD8339 particularly applicable in high density ultrasound scanners. In an ABF system, time domain coherency is achieved following the appropriate phase alignment and summation of multiple receiver channels. A reset pin synchronizes multiple ICs to start each LO divider in the same quadrant. Sixteen programmable 22.5° phase increments are available for each channel. For example, if Channel 1 is used as a reference and Channel 2 has an I/Q phase lead of 45°, then the user can phase align Channel 2 with Channel 1 by choosing the correct code.

The mixer outputs are in current form for convenient summation. The independent I and Q mixer output currents are summed and converted to a voltage by a low noise, high dynamic range, current-to-voltage (I-V) transimpedance amplifier, such as the AD8021 or the AD829. Following the current summation, the combined signal is applied to a high resolution analog-to-digital converter (ADC), such as the AD7665 (16-bit, 570 kSPS).

An SPI-compatible serial interface port is provided to easily program the phase of each channel; the interface allows daisy chaining by shifting the data through each chip from SDI to SDO. The SPI also allows for power-down of each individual channel and the complete chip. During power-down, the serial interface remains active so that the device can be programmed again.

The dynamic range is typically 160 dB/Hz at the I and Q outputs. The AD8339 is available in a 6 mm × 6 mm, 40-lead LFCSP and is specified over the industrial temperature range of −40°C to +85°C.

Applications