Resolving phase ambiguity

Question

The ADL5387 datasheet does not say if the part comes up in a "phase reset" state after power on. There is no dedicated reset pin for the part, nor a sync pin. I am trying to resolve 180 degree phase ambiguity between this part and another. Is there any way to do that with this part? The only way I can think of is to turn it on at the same exact 2XLO phase every time and then expect that it will start up at the same 1xLO phase. Is that reasonable or not?

enash · Accepted Answer

There is no mechanism in ADL5387 to guarantee a deterministic, “phase‑reset” LO state at power‑up, and the datasheet does not specify any defined initial phase for the internal ÷2 LO relative to the external 2×LO input. The LO path is a buffer followed by a divider that generates two quadrature carriers at half the input frequency, but no reset or sync control is provided, and no absolute phase behavior on start‑up is documented. The ÷2 function used to create the quadrature LO (implemented with flip‑flops and an inverter) inherently allows a 0°/180° ambiguity: the two valid internal states correspond to a global sign flip of I and Q, with the I/Q phase relationship itself remaining tightly controlled (small quadrature phase error as specified). This type of 0°/180° ambiguity due to LO dividers is also noted for other ADI parts and requires external calibration. [2][4] Because of that ambiguity, relying on “turn it on at the same exact 2×LO phase every time and expect the same 1×LO phase” is not a reasonable or guaranteed solution. You can expect repeatable I/Q relative phase on a given power cycle, but not a guaranteed absolute phase state versus the external LO across power cycles or across multiple devices. To resolve the 180° ambiguity between the ADL5387 and another device, the standard approach is system‑level calibration: use a known pilot tone or pattern, measure the complex baseband output, and if it appears inverted (≈180° shift), apply a digital sign flip to both I and Q for that channel. In multi‑channel systems, you can similarly compare channels to a reference and flip those that appear 180° out of phase. Once determined for a given power cycle, the state remains stable.)

SLA Status	Assignee	Support Status
SLA Closed. Met after 14 hours		Closed

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Resolving phase ambiguity

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