Product category:
Analogue and Mixed Signal ICs
News Release from: Texas Instruments (April 2001-March 2006) | Subject: OPA684
Edited by the Electronicstalk Editorial
Team on 01 November 2001
Low distortion from high-speed amps
The CFBplus OPA684 is the first current feedback amplifier from Texas Instruments to use an internally closed-loop input buffer stage to improve performance significantly.
The CFBplus OPA684 is the first current feedback amplifier from Texas Instruments to use an internally closed-loop input buffer stage to improve performance significantly over earlier sub-2mA quiescent current CFB amplifier products While retaining the benefits of very low power operation, this new architecture provides the benefits of a more ideal CFB topology
This article was originally published on Electronicstalk on 8 Nov 2004 at 8.00am (UK)
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"The OPA684 sets a new direction in high-speed amplifier design by providing outstanding bandwidth over a very wide gain range along with improved harmonic distortion compared to previous low power op amps", said Michael Steffes, strategic marketing manager for TI's high-speed signal processing products.
"This innovation steps up the performance of low power op amps by providing significantly reduced inverting input impedance while taking no added power penalty".
Steffes added: "Typically, when significant new levels of performance capability are created in the op amp universe, the full range of applications enabled by this innovation will only be limited by the imagination of the design community".
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The closed-loop input stage buffer provides a very low and linearised impedance path into the inverting input to sense the feedback error current that is fundamental to the operation of any CFB amplifier.
This improved inverting node impedance gives exceptional bandwidth retention to much higher gains and improved harmonic distortion over earlier solutions that were limited by inverting input linearity.
To illustrate, the OPA684 features a 210 to 120MHz bandwidth change from gains of 1 to 10 (200mV peak-peak, 100ohm load) - this is a 1.75:1 bandwidth variation over a 10:1 gain range.
The device gives more than 10dB improvement in total harmonic distortion (THD) at a gain of +2 (2V peak-peak, 100ohm load, 100kHz to 1MHz), compared to previous wideband CFB parts.
This improved distortion becomes even more dramatic at higher gains with the higher loop gain provided by the CFBplus amplifiers.
SFDR improves by more than 20dB at a gains above 10 versus earlier low power CFB amplifiers using open loop input buffer stages.
The output capability of the OPA684 also sets a new mark in performance for low power CFB amplifiers.
Delivering a full +/-4V peak-peak swing on +/-5V supplies, the OPA684 has the output current (>150mA) to support this swing into demanding filter or doubly terminated line loads.
This minimal output headroom requirement is complemented by a similar 1.2V input stage headroom, giving exceptional capability for single +5V operation.
The OPA684's low 1.7mA supply current is precisely trimmed at 25C.
This trim, along with low shift over temperature and supply voltage, gives a very robust design over a wide range of operating conditions.
System power may be further reduced by using the optional disable control pin.
Leaving this disable pin open, or holding it high, gives normal operation.
If pulled low, the OPA684 supply current drops to less than 130uA while the I/O pins go to a high-impedance state.
The single-channel OPA684 is sampling now, with production scheduled for 1Q02.
The OPA684 comes in SOT23-6 and SO-8 packages.
A dual channel version is scheduled for sampling in late 4Q01 and will be offered in an SO-8 package.
The OPA684 will be priced at $1.29 in 1000 piece quantities (suggested resale).
A lower power version, the OPA683, is also sampling now with production scheduled for 1Q02.
The OPA683 comes in a SOT23-6 and SO-8 packages.
A dual channel version is also scheduled for sampling in late 4Q01 and will be offered in an SO-8 package.
This 0.8mA supply current OPA683 will be priced at $1.15 in 1000 piece quantities (suggested resale).
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