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acquisitionZONE Products for the week of May 12, 2008
Texas Instruments Says…
ADS5560/62: 16-Bit, 40- and 80-Msample/s Data Converters Feature High Signal-To-Noise Ratio
Ultra-low noise floor and flexible digital features optimize performance in test and measurement, communications and imaging applications
Texas Instruments Incorporated (TI) introduced a family of 16-bit, single channel, 40- and 80-MSPS analog-to-digital converters (ADCs) which provide the highest signal-to-noise ratio (SNR) with very low power consumption. The devices’ low noise floor improves accuracy in test and measurement, receiver sensitivity in wireless communications, and image quality in medical, industrial and military applications.
The ADS5562, featuring a sample rate of 80 MSPS, and ADS5560, offering 40 MSPS, provide the highest signal-to-noise ratio (SNR) for input frequencies within the first Nyquist zone while consuming very little power. For instance, the ADS5562 offers 6 dB greater SNR and 0.6 more effective bits than any other 80-MSPS device consuming less than 900mW of power. The device also offers dynamic power scaling, reducing power consumption to as little as 540mW at 25 MSPS.
EN-Genius Says…
Wow, TI is going for the jugular with this one! The emphasis is on noise, but they might equally well have made it about power – but a little more cautiously.
Let’s remind ourselves of that well-worn, and often taken out of context, equation for theoretical SNR in ADCs: SNR = 6.02n + 1.76 dB, where n is the number of bits. For a 16-bit ADC that works out at 98.08 dB. When you look at TI’s competition for 80 Msample/s parts there are three parts from ADI that give SNRs of 78.4 dB for the AD9460-80, 81.8 dB for the AD9446-80, and 80.5 dB for the AD10678. But those parts consume 1.8 W, 2.6 W, and 8 W, respectively.
Similarly, from Linear, the LTC2206 gives an SNR of 78.2 dB but has a wonderfully low consumption of 650 mW.
The full news release from TI quotes an analog power consumption of 693 mW...but, as always, beware of the small print. If the part is being used with CMOS outputs the total power consumed will be 891 mW, and 869 mW using the LVDS outputs. That puts the part between the Linear lowball and the ADI highballs.
The SNR claimed by TI (with a 3 MHz input) is 81.4 dBFS, typical, using the CMOS outputs and 84 dBFS using the LVDS outputs. They go on to talk about another improvement with a flicker noise suppressor, operating to about 1 MHz, which gives a further 4.2 dB improvement in low frequency SNR: up to 95.9 dBFS is claimed in a table in the full news release. I have no idea what that means in relationship to the good old SNR equation, but I am not comfortable with the numbers.
The improvement in SNR with LVDS outputs appears to have no effect on SINAD which the data sheet gives (all at 3 MHz input) as both 80.5 dBFS for LVDS and 80.5 dBFS for CMOS. SFDR is 85 dBc and the second harmonic is -90 dBc. IMD with tones at 5 MHz and 10 MHz at -7 dBFS, is -92 dBc.
In dc accuracy terms the ADS5562 offers 0.5LSB DNL, ±3LSB INL and ±10 mV offset error.
The differential analog input range is 3.56 Vpp with an input bandwidth of 300 MHz and an input common-mode current of 6.6 µA/Msample/s per input pin. TI has provided a programmable fine gain control of 6 dB in 1 dB steps. There is no location for this gain control shown in the block diagram but it allows for the input to be scaled down to 2 Vpp. The voltage reference is on-chip. A differential clock input drives an on-chip generator.
How well will these parts do? There are some applications where lack of noise is everything and the ADS5562 and the ADS5560 will do particularly well in medical imaging and test and measurement areas, although there are other markets that will also benefit. With the commanding lead that TI has in SNR – and I hope to understand the 1/f thing after my next visit to Tucson – they can dominate the market. They are priced right, they have a minimal number of pins, and they are coming from a respected source for high-speed ADCs. Look out too for other 16-bit parts coming at up to 135 Msample/s.
The ADS5560 and ADS5562 are in production in thermally-enhanced QFN-48 priced at $35.00 and $48.33, respectively, in 1000-piece lots.
Data Sheet
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