acquisitionZONE Products for the week of March 17, 2003
The combination of high-speed and high-precision is ideal for demanding measurement requirements in scientific instrumentation, automated test equipment, data acquisition, medical imaging and vibration analysis.
"The ADS1605 is twice as fast as the nearest delta-sigma competition and has roughly a 10 to 15dB advantage in the key performance areas of SNR, THD and SFDR over competitive devices utilizing other architectures. And when measuring small input signals, it further outperforms the competition with unprecedented low-level THD and SFDR," said Jim Todsen, product line manager for TI's oversampling data converter products. "The ADS1605 is also the lowest priced solution within this performance segment."
The breakthrough speed and performance offered by the ADS1605 further illustrates TI's industry-leading data converter expertise and builds upon several recent advanced data converter developments:
analogZONE Says . . .
The ADS1605 represents a real jump in data rate for delta-sigma ADCs at the 16-bit level of resolution. TI even needs to enter a 16-bit category in its >1 MSPS (sic) category in its online product tree. (At the same time somebody can remove the 1-bit ADS1202 motor control delta-sigma modulator from the 16-bit resolution ADC category in the company's parametric search.) But achieving speed is not important if the other specifications aren't held to the same standard. The ADS1605 does not disappoint. The dynamic specifications are really nice.
The ADS1605 is an 8x oversampling delta-sigma ADC with a 2-1-1 MASH architecture and a simple parallel data output. With clocking at 40 MHz the digital filter decimates the output to provide data output words of 5 Msample/s and a signal passband out to 2.45 MHz (-3 dB.) The decimation rate can be changed by pin logic to 4 which would reduce group delay and settling times, but it would also reduce the SNR by a theoretical 3 dB. A 1.57-V reference to the modulator is a scaled version of that generated on-chip and this can be overdriven by an external source: External buffers are recommended.
Like most delta-sigma ADCs the external signals driving the part need to be able to charge the internal capacitors in half the sampling period; with a 40-MHz clock that is within 12 ns. This is a part that is designed to be driven differentially to achieve the best performance. Passband ripple is within ±0.0025 dB out to 2.2 MHz and this passband is repeated as positive and negative sidebands at harmonics of the 40-MHz clock. Because the modulator bandwidth is out to 100 MHz care must be taken to remove any noise on the input that might be in the 40- and 80-MHz regions - any such noise will be aliased back-in-band to reduce the SNR.
There are three supplies on the ADS1605: Analog, digital and digital I/O. The last two can be connected together if they use the same voltage (the digital I/O can be powered from 2.75 V to 5.25 V.) With the analog rail at 5 V the quiescent is a typical 110 mA, while with the digital and digital I/O rails at 3 V those parts draw 45 mA and 4 mA, both typical, respectively.
It is nearly impossible to do any real apples-to-apples comparison of dynamic performance with this and other ADCs but typical numbers for a 100-kHz input at -2 dBFS are 88 dB for SNR, -93 dB for THD, 86 dB for SINAD, and 96 dB for SFDR. With a 2-MHz input (-2 dBFS) the same numbers are 84 dB, -98 dB, 84 dB, and 102 dB. All these are close to maximal for the resolution. The IMD with signals at 1.99 MHz and 2.00 MHz, both at -2 dBFS, is an impressive 94 dB.
I have no doubt at all that this part will push the next generation of scientific instruments, medical imaging systems and vibration analysis. It has also been priced to attract a lot of attention from those designers.
The ADS1605 is in production now in a thermally-enhanced TQFP-64. It is priced at $32.05 in 1000-piece lots.