acquisitionZONE Products for the week of June 7, 2004
The AD8139 is the only diff amp available today that simplifies the challenge of driving 16-and 18-bit, high-speed ADCs with its optimal combination of low noise, low distortion and rail-to-rail output.
The AD8137 is the market's lowest-power, lowest-cost, high-speed diff
amp for driving 12-bit battery-operated data acquisition systems and other
systems sensitive to power and cost.
analogZONE Says . . .
The AD8139 is the gem here with a very interesting combination of features intended to drive high resolution ADCs with close to output rail (within 150 mV to 200 mV) performance maximizing dynamic range. I would normally expect noise performance at 1 nV/rtHz or better for 18-bit performance, instead of the 1.9 nV/rtHz here, but the increased dynamic range makes up for that. In addition the other dynamic performance criteria are superb.
Dynamic performance is better (and smoother) with split 5-V rails giving a large signal (2 Vpp) bandwidth of typically 240 MHz and an 0.1-dB flatness of 45 MHz. The slew rate (2-V steps) is a typical 800 V/µs and the settling time is 45 ns.
SFDR with a 2-Vpp signal is 98 dB at 1 MHz and 72 dB at 20 MHz (99 dB and 75 dB with a single 5-V rail), while third-order IMD (tones at 10 MHz and 10.1 MHz) is -90 dBc (-87 dBc with a single rail). CMRR is 88 dB with split rails and PSRR is at about 110 dB. These numbers require current, of course, and the AD8139 takes a little over 20 mA.
The data sheet kind of contradicts itself over the noise performance but a graphical characteristic clearly shows that after the 1/f corner the input voltage noise is at better than 2 nV/rtHz from about 1.2 kHz to about 50 MHz. The data sheet is, on the other hand, very detailed about source impedances and common-mode issues.
The AD8139 will not only find differential input/output use for driving high-resolution ADCs, it will also find uses for high-quality single-ended to differential conversion and as a level shifter in applications where the quality can demand the price premium. The output can drive in excess of 80 mA so it may also find homes in differential cable drivers up to maybe 30 MHz.
The AD8139 is in production in a thermally enhanced SOIC-8 and sampling in a LFCSP-8 priced at $3.59 in 1000 piece lots. The lower performance AD8137, but drawing only 1.8 mA is also in production in SOIC-8 and sampling in LFCSP-8 and is priced at $1.09 in 1000-piece lots.
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Sheet (AD8137)
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Sheet (AD8139)