Wednesday, February 29, 2012

AD9279 - Octal LNA/VGA/AAF/ADC and CW I/Q Demodulator

The  AD9279 is designed for low cost, low power, small size, and ease of use for medical ultrasound and automotive radar. It contains eight channels of a variable gain amplifier (VGA) with a low noise preamplifier (LNA), an antialiasing filter (AAF), an analog-to-digital converter (ADC), and an I/Q demodulator with programmable phase rotation.

Each channel features a variable gain range of 45 dB, a fully differential signal path, an active input preamplifier termination, and a maximum gain of up to 52 dB. The channel is optimized for high dynamic performance and low power in applications where a small package size is critical.

The LNA has a single-ended-to-differential gain that is selectable through the SPI. Assuming a 15 MHz noise bandwidth (NBW) and a 21.3 dB LNA gain, the LNA input SNR is roughly 94 dB. In CW Doppler mode, each LNA output drives an I/Q demod-ulator that has independently programmable phase rotation with 16 phase settings.

Power-down of individual channels is supported to increase battery life for portable applications. Standby mode allows quick power-up for power cycling. In CW Doppler operation, the VGA, AAF, and ADC are powered down. The ADC contains several features designed to maximize flexibility and minimize system cost, such as a programmable clock, data alignment, and programmable digital test pattern generation. The digital test patterns include built-in fixed patterns, built-in pseudo random patterns, and custom user-defined test patterns entered via the serial port interface.

AD9279 Main Features:
1. 8 channels of LNA, VGA, AAF, ADC, and I/Q demodulator
2. Low power: 141 mW per channel, TGC mode, 40 MSPS;
3. 60 mW per channel, CW mode
4. 10 mm × 10 mm, 144-ball CSP-BGA
5. TGC channel input-referred noise: 0.8 nV/√Hz, max gain
6. Flexible power-down modes
7. Fast recovery from low power standby mode: <2 μs
8. Overload recovery: <10 ns
9. Low noise preamplifier (LNA)
10. Input-referred noise: 0.75 nV/√Hz, gain = 21.3 dB
11. Programmable gain: 15.6 dB/17.9 dB/21.3 dB
12. 0.1 dB compression: 1000 mV p-p/ 750 mV p-p/450 mV p-p
13. Dual-mode active input impedance matching
14. Bandwidth (BW): >100 MHz
15. Variable gain amplifier (VGA)
16. Attenuator range: 45 dB to 0 dB
17. Postamp gain (PGA): 21 dB/24 dB/27 dB/30 dB
18. Linear-in-dB gain control
19. Antialiasing filter (AAF)
20. Programmable second-order LPF from 8 MHz to 18 MHz
21. Programmable HPF
22. Analog-to-digital converter (ADC)
23. SNR: 70 dB, 12 bits up to 80 MSPS
24. Serial LVDS (ANSI-644, low power/reduced signal)
25. CW mode I/Q demodulator
26. Individual programmable phase rotation
27. Output dynamic range per channel: >160 dBc/√Hz
28. Output-referred SNR: 155 dBc/√Hz,1 kHz offset,3 dBFS

Figure 1: AD9279 Functional Block Diagram

AD9279 Functional Block Diagram

Figure 2: AD9279 Single Simplified Block Diagram
AD9279 Single Simplified Block Diagram

Figure 3: AD9279 Simplifies Block Diagram of the Ultrasound System
AD9279 Simplifies Block Diagram of the Ultrasound System

Figure 4: AD9279 Transformer-coupled Differential Clock Circuit
AD9279 Transformer-coupled Differential Clock Circuit

Figure 5: AD9279 Differential PECL Sampling Clock Circuit
AD9279 Differential PECL Sampling Clock Circuit

Figure 6: AD9279 Differential LVDS Sampling Clock Circuit
AD9279 Differential LVDS Sampling Clock Circuit

Figure 7: AD9279 Single-ended 1.8V CMOS Sampling Clock Circuit
AD9279 Single-ended 1.8V CMOS Sampling Clock Circuit

Figure 8: AD9279 Single-ended 3.3V CMOS Sampling Clock Circuit
AD9279 Single-ended 3.3V CMOS Sampling Clock Circuit

Figure 9: AD9279 CW Mode I / O Output Interface to Connect a Typical Circuit

AD9279 CW Mode I / O Output Interface to Connect a Typical Circuit

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