Design Con 2015

TI lowest-power octal, 100-MSPS ADC for medical, industrial imaging applications

-February 12, 2013

Texas Instruments introduced an octal, 12-bit, 100-MSPS analog-to-digital converter (ADC) that provides the lowest power consumption in its class. The ADS5295 uses less than 80 mW per channel, which diminishes board heat and power dissipation in higher-channel-density applications. It incorporates TI’s digital processing block, which combines commonly used digital functions to help improve signal-to-noise ratio (SNR) and filter harmonics while reducing output data rate for narrow-band applications. 

The ADS5295 can be used in phase-array architecture systems with higher channel counts, such as ultrasound, security x-ray and non-destructive testing (NDT) applications. 

I like the input structure of this device. Some really good design effort went into this switched-capacitor based structure. This differential topology results in a very good ac performance even for high input frequencies at high sampling rates. See Figure 1.


Figure 1: Analog input equivalent circuit is shown here (Courtesy of TI)

 

Driving the input is critical to common-mode noise immunity and even-order harmonic rejection due to a differential drive structure. DC-coupled (Figure 2) and AC-coupled (Figure 3) are shown below. Figure 3 shows a small 10 ohm resistor in series with the differential inputs to damp our ringing due to package parasitics. The R-C filters shown across the analog input pins in Figures 2 and 3 absorbs the glitches caused by the opening and closing of the input device sampling capacitors.

 

Figure 2: The cicuit shown is for a DC-coupled drive circuit with RCR (Courtesy of TI)

 

 

Figure 3: The circuit shown is for an AC-coupled drive circuit (Courtesy of TI)

 

Key features and benefits of the ADS5295

  • Lowest power per channel for the speed, with low noise: Using only 80 mW-per-channel at 100 MSPS and eight channels, it enables designers to increase channel count without increasing power dissipation high-density applications, while still achieving a low noise of 71 decibel full scale (dBFS) SNR.
  • Reduced system cost and complexity: TI’s highly integrated digital processing block integrates commonly used digital functions, such as a low-frequency noise suppression mode, digital filtering options and programmable mapping of low-voltage differential signaling (LVDS) output pins. This lowers FPGA cost and simplifies LVDS output routing, reducing the number of printed circuit board (PCB) layers and bill of materials cost.
  • Reduced interface lines: Outputs data over one or two wires of LVDS pins per channel, reducing the number of interface lines. This creates a two-wire interface, which keeps the serial data rate low to further reduce FPGA cost.

 

Tools and support

 

An evaluation module (EVM) is available to test the ADS5295 under a variety of conditions. The ADS5295EVM is priced at US$299. An IBIS model to verify board signal integrity requirements is also available.

Pricing and package

The ADS5295 is in an 80-pin HTQFP package for a suggested retail price of US$70 in quantities of 1,000.

Optimized analog products and full portfolio for imaging applications

The ADS5295 joins the ADS529x family, which includes the 14-bit ADS5294 and 12-bit ADS5292. These devices offer eight channels at 80 MSPS, with 77-dBFS and 72-dBFS performance, respectively.

For more information visit TI’s website

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