High Current Driver Amplifier and Digital VGA/Preamplifier with 3 B Steps

The AD8260 includes a high current driver, usable as a transmitter, and a low noise digitally programmable variable gain amplifier (DGA), useable as a receiver.

The receiver section consists of a single-ended input preamplifier, and linear-in-dB, differential-output DGA. The receiver has a small signal –3 dB bandwidth of 230 MHz; the driver small signal bandwidth is 195 MHz. The driver delivers ±300 mA, well suited for driving low impedance loads, even when connected to a 3.3 V supply.

The AD8260 DGA is ideal for trim applications and has a gain span of 30 dB, in 3 dB steps. Excellent bandwidth uniformity is maintained across the entire frequency range. The low output-referred noise of the DGA is advantageous in driving high speed ADCs. The differential output facilitates the interface to modern low voltage high speed ADCs.

Single-supply and dual-supply operation makes the part versatile and enables gain control of negative-going pulses, such as those generated by photodiodes or photo-multiplier tubes, as well as processing band-pass signals on a single supply. For maximum dynamic range, it is essential that the part be ac-coupled when operating on a single supply.

The AD8260 preamplifier (PrA) is configured with external resistors for gains greater than 6 dB and can be inverting or noninverting. The DGA is characterized with a noninverting preamplifier gain of 2×. The attenuator has a range of 30 dB and the output amplifier has a gain of 8× (18.06 dB). The lowest noninverting gain range is −6 dB to +24 dB and shifts up with increased preamplifier gain. The gain is controlled via a parallel port (Pin GNS0 to Pin GNS3) with 10 gain steps of 3 dB per code. The preamplifier and DGA are disabled for any code that is not assigned a gain step.

The AD8260 can operate with single or dual supplies from 3.3 V to ±5 V. An internal buffer normally provides a split supply reference for single-supply operation; an external reference can also be used when the VMID buffer is shut down.

The operating temperature range is −40°C to +105°C. The AD8260 is available in a 5 mm × 5 mm, 32-lead LFCSP.

Applications

* Digital AGC systems

* Tx/Rx signal processing

* Power line transceivers

* High current driver

* Differential input—direct drive from DAC

* Preset gain: 1.5×

* −3 dB bandwidth: 195 MHz

* Large output drive: >±300 mA

* VGA/preamplifier

* Low noise

Voltage noise: 2.4 nV/√Hz

Current noise: 5 pA/√Hz

* −3 dB bandwidth: 230 MHz

* Gain range: 30 dB in 3 dB steps

−6 dB to +24 dB (for preamplifier gain of 6 dB)

* Single-ended preamplifier input and differential VGA output

* Supplies: 3.3 V to 10 V (with VMID enabled)

* ±3.3 V to ±5 V (with VMID disabled)

* Power: 93 mW with 3.3 V supplies

* Power-down for VGA, driver amplifier, and system