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Eight-channel, high-speed ADCs with serial LVDS interface has 70.5 SNR

Establishing a new standard for integration, performance and power, Texas Instruments Incorporated (TI) announced a family of octal, 10- and 12-bit, high-speed analog-to-digital converters (ADCs) from the company's Burr-Brown product line. Featuring serial low-voltage differential-signaling (LVDS) outputs and consuming 123mW of power per channel at 65 MSPS (138mW/channel at 70 MSPS), the ADS527x family offers the lowest power of any competitive product. The devices allow high system density in ultrasound, wireless communications, optical networking, instrumentation, test and measurement, and a variety of other multi-channel applications.

“The innovative ADS527x family offers the highest level of integration and performance by providing eight parallel, 12-bit ADCs with 70.5dB SNR at 70MSPS. By combining this integration with the lowest power per channel of competitive products, the ADS527x will enable higher channel counts and higher performance in applications such as ultrasound, PET scanners and numerous other imaging and communications systems,” said Ed Fullman, product marketing manager for TI's high-speed data converter products. “Ultimately, these devices will allow designers to integrate more channels into smaller, more affordable systems ” enabling advanced diagnostics in a broader range of environments around the world.”

The ADS527x family includes 40, 50, 65 and 70 MSPS (mega samples per second) versions in 12-bit resolution, and 40, 50 and 65 MSPS versions in 10-bit resolution. All products in this family are both pin and serial LVDS compatible, providing a simple upgrade path in both sample rate and resolution.

Serial LVDS greatly simplifies the ADC interface and allows for compatibility between the different family members in terms of speed and resolution. TI's implementation of serialized LVDS offers the user the flexibility to optimize interface power dissipation based on system requirements, and is compatible with Xilinx and Altera programmable devices. Xilinx deserializer source code is available as a free license from Texas Instruments when used with TI data converters.

The ADS527x family is optimized to work with TI's high-performance TMS320C6000 DSP platform, which is used in applications ranging from high-resolution medical imaging to third-generation wireless communications infrastructure. In addition, depending on the application requirements, the ADS527x family is optimized for pairing with many of TI's high-speed op amps to achieve highest performance.

The integration, performance and power of the ADS527x family will allow imaging systems, such as ultrasound, to improve image quality with exceptional 12-bit, 70.5dB SNR performance, reduce power requirements, increase channel density and decrease board space demands.

In wireless communications systems, such as base stations and pico-cells, the ADS527x family will improve system performance by reducing system complexity, handling more voice channels, reducing system form factors, increasing flexibility and lowering operating costs.

The ADS527x family offers exceptional signal-to-noise ratio (SNR) of 70.5dB (60.5dB for the 10-bit family) at 10MHZ input frequency. The devices provide internal references to simplify system design requirements, or can be driven with external references. The ADS527x family operates from a 3.3V supply.

All eight channels share a common sample clock for excellent skew and jitter performance. Individual power down of each ADC channel enables optimized operation. A peak-to-peak differential input range of 2V maintains signal integrity, and a common internal or external voltage reference allows excellent matching between channels.

ADS5273 — 12bit — 70MSPS — $121.00
ADS5272 — 12bit — 65MSPS — $65.00
ADS5271 — 12bit — 50MSPS — $50.00
ADS5270 — 12bit — 40MSPS — $45.00
ADS5277 — 10bit — 65MSPS — $40.00
ADS5276 — 10bit — 50MSPS — $36.00
ADS5275 — 10bit — 40MSPS — $32.00

Texas Instruments Incorporated Semiconductor Group, SC-04020 Literature Response Center P.O. Box 954 Santa Clara, CA 91380 Tel: 800-477-8924
www.ti.com

These seven A/D converters from TI are similar to the ADS5500 that I reviewed a couple months ago, but there are some important differences. For example, the new 527x family members are octal ADCs and have serialized LVDS outputs. Additionally, they have 10- and 12-bit resolution compared to the 14-bit for the 5500, and the sampling rates are slower, ranging from 40 to 70 MSPS compared to the 125MSPS for the ADS5500. These differences, however, are designed differences to help them meet different requirements for different markets. The eight channel outputs in the ADS527x family are important for applications that need additional channel capabilities like ultrasound and wireless base stations. Also, the family includes serialized LVDS output, which seems to be the up-and-coming standard for high-speed data converters used in imaging and wireless communications.

The noise spec for the 527x is pretty impressive and TI says it is seeing 70.5 dB SNR as typical. Achieving 70.5 SNR at the 123mW power levels is impressive. You can find 65MHz, 12-bit ADCs on the market that have good SNR, but they don't come close to the power level provided by TI. For data converters, power is the number one spec for improving SNR. So achieving high SNR and low power is a significant accomplishment.

However, there is a trade off when you try to improve SNR. Typically, manufacturers increase the size of the sampling capacitors on the input sample and hold (S/H), because it has a direct relationship on how much power is consumed. The S/H circuit consumes the most power of any part of the design. Unfortunately, increasing the size of the sampling capacitors will increase the power consumption significantly. TI managed to balance these design techniques and use a superior process technology to create a device with impressive specs. The converter also uses a typical, single 3.3V supply, and supports a 2Vp-p input swing, which is unusual for a 0.18um process.

Finally, all members of this family are pin and format compatible. The LVDS interface is compatible for the 10- and 12-bit versions. That means the parts are interchangeable and you don't have to change the deserializing software or code because everything runs exactly the same way. It also is source synchronous where you have a separate frame clock and LVDS clock and data. The LVDS interface, although it has complicated timing diagrams, becomes very simple once you have solved the timing issues. Solving these timing issues isn't trivial so TI offers some tips to make it easier for designers. The LVDS interface is worth the trouble because it's a robust interface that is immune to noise, which is a problem for many designers. Additionally, the user can program the LVDS interface from 3.5mA to 6 mA. The default is 3.5mA but if you want to transmit long distances and you have a lot of resistance in the signal path you may want to boost the current. There are also different patterns allowed to debug the interface such as MSB first or LSB first. TI says it has run simulations up to 1 meter at 3.5mA.

You may wonder what this product can do for the end equipment. For imaging products such as ultra sound it means that you can improve the quality of the image. The improved quality is derived from the improved SNR performance, and increasing the channel count, which means the equipment uses more channels to improve the picture quality. So, higher density means manufacturers can integrate more channels in the system, and for portable systems it means increased battery life.

Evaluation modules are provided and that's important because it provides the end-customer a way to look at the data. Most customers don't have a way to deserialize the data and this helps the customer design in this product and interface. TI developed an analog board for each product in the family and has a deserializer board for the data and puts it in a standard format. TI made this board with a Xylinx-based format and is also working on one in an Altera-based format. So, that means TI takes their design kits and develops the code for you. The code is available to customers through a no-charge license so it can be integrated into the customer's programmable devices. However, this is available if the customer uses TI's ADCs.

The data sheets for the 5270, 71, and 72 appear to be exactly the same and even provide information for all three parts on each of them, so I don't know why TI made it confusing by having three URLs for identical information. The same is true for the 5275, 76, and 77 data sheets. If you need to access a specific data sheet you just have to change the part number in the URL string.

Samples and EVMs (Evaluation Modules) of ADS527x family are available now with volume production scheduled for March 2004. The devices are packaged in an 80-lead TQFP.

Data sheets:
12-bit 70 MSPS ADS5273
12-bit 40, 50, 65MSPS ADS5270, 71, 72
10-bit 40,50, 65MSPS ADS5275, 76, 77

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