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Need help with the ADN2812

Question asked by ttranter on May 19, 2015
Latest reply on May 19, 2015 by Dongfeng

From a customer:

 

What we're seeing is the ADN2812 lock on harmonics of the signal of interest but not the fundamental - we need to understand better what this device requires in terms of spectrum/waveform. And perhaps the input levels and SLICE function (datasheet isn't clear exactly what this input does)

... More detail.

 

- We're driving a pulsed laser into a Picometrix AT-2.5SFA receiver (photo diode/amp). Out of this device and into the ADN2812 (which is the ADI eval board) we have a pulse of varying shape depending on optic power and whether the Picometrix amp is saturating. In some cases the ADN2812 doesn't lock; in other cases it may lock on the 3/2x, 2x, or 3x harmonic (our operating frequency is 1.25GHz (Gbps)).

 

- The desired, non-saturated signal from the receiver is a 300-400mV pulse ~200pS wide. In this case the 2812 generally doesn't lock (output is ~3.0Ghz). If the input power is raised to the point of saturating the receiver, we get a fast edge up, followed by a slow ramp down as the amp recovers. In this case we're able to lock at 2x the desire frequency.

 

- We're thinking the ADN2813 or 2815 may help as these devices are band limited at 1.25GHz - but we need a better understanding of whats going on though either way. Everything is driven deferentially and we are using the 1.5uF caps that were standard on the eval for coupling the input.

 

A conference call to discuss or emailed thoughts welcome ... Jim

 

(Stacey, in hind-sight we should have captured the waveforms before I left today - maybe we can do that tomorrow via phone. The scope can print to a thumb drive and should come up configured as it was when we powered it down)

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