ADC driving DC-10GHz differential amplifier has digital control

ADL5580 is a SiGe dc to 10.0GHz differential-in differential-out gain block from Analog Devices, which has a digital bus for signal path tweaking.

“The amplifier offers a referred-to-input noise spectral density of 2.24nV/√Hz at 1GHz and is optimised for distortion performance over a wide frequency range, making the device ideal for driving high speed 12bit to 16bit ADCs,” according to distributor Anglia, which is currently promoting the part.

Gain is internally set to 10dB, but can be reduced by adding two resistors. At 1GHz, the input stage has an 11.3dB noise figure. Input impedance is 100Ω differential and the output impedance is 50Ω differential.

Accordig to ADI, configured as a differential-in differential-out amplifier with 1.4Vp-p on the input, distortion figures are:

2GHz: -59.4dBc (HD2), -54.3dBc (HD3), -68.2dBc (IMD3)
6GHz: -66dBc (HD2), -88.1dBc (HD3), -48.3dBc (IMD3)

This is with supply rails of +5V (~276mA) and -1.8 V (~-224mA) and a 50Ω load in parallel with 1pF – a disable input drops consumption to 2mA.

The amplifier is suited to “driving a variety of ADCs, mixers, pin diode attenuators, surface acoustic wave filters and a multiplicity of discrete RF devices,” said ADI. “The output impedance allows users to drive ADCs like the AD9213 directly without any matching networks, that is at a 50Ω differential input. For load conditions other than 50Ω differential, external termination networks are required.”

The 1.4V maximum maximum input amplitude of the AD9213 also matches the maximum signal handled by the amplifier.

On top of this, Anglia sees the gain block being used in zero IF and complex IF receiver designs.

Digital control

An SPI interface allows the user to enable blocks and alter the signal path.

Register bits allow the output common mode voltage to be sourced internally (with a choice of 410, 510, 600 or 700mV) or brought in from outside the chip (through the ‘VCMO’ pin). If it is internally sourced, there is an option to export this voltage for external use through the same pin.

The input common mode voltage it treated similarly, except the choice is 1.39, 1.53. 1.67 or 1.80V, and the associated analogue IO pin is ‘VCMI’.

Other registers are available to optimise gain flatness/peaking and RF bandwidth.

Operation is over -40 to +85°C and it comes in a 4 x 4 mm 20pad LGA package.

ADL5580-EVALZ is the associated evaluation board.

Anglia’s promotion page is here.