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Current feedback amplifier targets high-speed apps

Posted: 17 Jun 2008     Print Version  Bookmark and Share

Keywords:current feedback amplifier  bandwidth gain  signal conditioning  differential amplifier 


Texas Instruments Inc. has introduced a dual-channel, high-speed current feedback amplifier that features 70 per cent greater bandwidth gain at +2V/V than competitive devices. The device provides fast signal conditioning with the highest linearity to minimise distortion for better signal fidelity and easier filtering.

It offers wide supply voltage options and large gain capability, giving engineers the flexibility to adjust the parameters to address the specific need, such as high gain for differential signals or high output voltage or current for low power consumption. In addition, the device's optimised symmetrical package eases layout for cost-effective precision IF amplifiers, high-speed arbitrary waveform output drivers, wideband ADC drivers and active filters.

Current feedback architecture
Unlike traditional voltage feedback or fully differential amplifiers, the OPA2695 offers a new level of performance for high-speed applications. Due to its current feedback architecture, the OPA2695 can deliver a high bandwidth of 850MHz at a gain of +2V/V and a fast slew rate of 2,900V/µs to process high-speed signals.

The architecture also provides wider bandwidth capability at much higher gains than can be achieved with a voltage feedback architecture. In contrast, fully differential amplifiers, which are popular for differential signal paths and are based on voltage feedback architecture, suffer from reduced bandwidths at larger gains.

The OPA2695 combines the current-feedback architecture with an optimised differential pin-out, which provides superior gain and bandwidth, maintains high linearity with low harmonic distortion levels, and eases the design process. The pin-out gives super-symmetrical signal paths with input and output pins on opposite sides of the chip to greatly simplify PCB layout.

Moreover, the optimised pin-out enables superior even-order harmonic distortion, which cannot be achieved by other current feedback devices with traditional pin-out configurations. The OPA2695 provides second-order harmonics (HD2) of 94dBc and third-order harmonics (HD3) of 93.5dBc at 10MHz for differential signals, and HD2 of better than 90dBc up to 55MHz at a large gain of +10V/V, which reduces in-band harmonic distortion while easing the filtering of out-of-band even order harmonics.

Supply voltage options
In addition, designers have the flexibility to provide a single supply voltage (3.5-12V) or a dual supply voltage (±1.75V to ±6V) to the OPA2695 to suit their requirements. For example, with a supply voltage of ±5V and gain of 8V/V, the OPA2695 can deliver a large output voltage swing of ±4.1V or 8.2Vpp with a 120mA sourcing or sinking output drive current into an ADC for accurate digitisation.

Alternatively, at a lower single supply voltage of 5V, the device can save power while still delivering ±90mA output current with a 3.4Vpp for power-sensitive applications, such as handheld portable devices. To further reduce power consumption, a power down option is also available, which reduces the quiescent current consumption to 80µA.

The OPA2695 extends TI's high-speed, current feedback amplifier portfolio, which offers the industry's widest bandwidth.

The OPA2695 is available today in a SO-8 and QFN-16 package. Suggested resale pricing is Rs.84.04 ($2.10) in quantities of 1,000. Samples and evaluation modules of the OPA2695, single-channel OPA695 and triple-channel OPA3695 are also available.

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