ADI creates internal silicon PCB for system-in-package ADCs

To increase system-in-package integration density, Analog Devices is stacking die on a passives-on-silicon substrate using technology developed at its Limerick design centre.

Dubbed iPassive, “this is a new thing in system-in-package”, ADI field application engineer Thomas Tzscheetzsch told Electronics Weekly at Embedded World in Nuremberg. “The passives are in the silicon, not in poly, real silicon. They are matched to 0.1%, with temperature drift in the same direction, and have 1% absolute accuracy over temperature: -40 to +125 or -40 to +105°C.

iPassive has been used to add a matched input driver and a reference buffer to the firm’s 4000 series of high-accuracy successive approximation ADCs (see photo), forming the yet-to-be-released ADAQ400x series which will sample at rates around 1-2Msample/s with 16 or 18bit resolution.

Adding an input buffer to the package greatly eases driving the variable input impedance of the converter.

According to Tzscheetzsch, it has a fast rise-time, settling to 0.1% “within several nanoseconds, and you can power down the amplifier while the ADC is converting”.

Power is 7mW/Msample/s for the ADC and ~1mA for the buffer.

Because of the iPassive substrate, ADI will be offering custom versions if the quantities are high enough (>50-100,000, said Tzscheetzsch).

This is a dual-supply product, Last year the firm released the similar ADAQ798x series which accepts only single-ended inputs and does not use iPassive.