Transmitter linearity built-in-self-test

An apparatus for testing a circuit, comprising:

• a transceiver having a transceiver input and a transceiver output;
• a two-tone source coupled to the transceiver input;
• and
• an adjacent channel power ratio (ACPR) estimator coupled to the transceiver output and coupled to the two-tone source, the ACPR estimator
• configured to calculate coefficients of a polynomial representation of an output signal of the transceiver output, to apply stored weight factors to the coefficients to calculate an ACPR value the stored weight factors corresponding to a main channel frequency range and an adjacent channel frequency range, and
• configured to determine whether the ACPR is within an acceptable range and generate a corresponding indicator.

A method of testing a circuit comprising:

• receiving an evaluation signal from a transceiver;
• calculating a plurality of polynomial coefficients for a polynomial expression corresponding to the evaluation signal;
• selecting a set of first weight factors according to a main channel frequency range;
• applying the set of first weight factors to the plurality of polynomial coefficients to obtain a main channel power;
• selecting a set of second weight factors according to an adjacent channel frequency range;
• applying the set of second weight factors to the plurality of polynomial coefficients to obtain an adjacent channel power;
• calculating an Adjacent Channel Power Ratio (ACPR) value from a ratio of the adjacent channel power to the main channel power;
• and
• determining whether the ACPR value is within an acceptable range and generating a corresponding indicator.