Wireless Circuitry with Loopback Path All-Pass Filters

An electronic device comprising:

• processor circuitry;
• at least one antenna;
• a transmit path that couples the processor circuitry to the at least one antenna;
• a receive path that couples the at least one antenna to the processor circuitry;
• a loopback path that couples the transmit path to the receive path;
• and
• a passive all-pass filter interposed on the loopback path between the transmit path and the receive path.

A loopback path for conveying differential radio-frequency signals from a transmit path in a radio-frequency transceiver to a receive path in the radio-frequency transceiver, the loopback path comprising:

• a first signal line coupled to the transmit path;
• a second signal line coupled to the transmit path, the first and second signal lines forming a differential pair of signal lines;
• an all-pass filter having a first input terminal coupled to the first signal line, a second input terminal coupled to the second signal line, a first output configured to output the differential radio-frequency signals with a first phase, and a second output configured to output the differential radio-frequency signals with a second phase that is 90 degrees out-of-phase with respect to the first phase;
• and
• a multiplexer having a first input coupled to the first output of the all-pass filter, a second input coupled to the second output of the all-pass filter, and a third output communicably coupled to the receive path, the multiplexer having a first state in which the first input is coupled to the third output and having a second state in which the second input is coupled to the third output.