Gain imbalance compensation method and apparatus for a quadrature receiver

In a cordless telephone having a base station connectable to a switched telephone network and at least one handset and at least one handset, said base station and handset communicating over a radio frequency link utilizing time division duplex direct sequence quadrature modulation, a gain imbalance compensation circuit in said handset and in said base station, each connected to receive the digital in-phase and quadrature baseband signals received over the radio frequency link, the gain imbalance compensation circuit comprising:

• a circuit for introducing a frequency offset signal into the in-phase and quadrature signal channels during the time the handset is in the cradle of the base station;
• a first digital circuit for detecting a gain imbalance between the resulting signals in the in-phase and quadrature channels;
• and
• a second digital circuit for increasing or decreasing the gain in the in-phase and quadrature signal channels until the gain in the in-phase and quadrature channels are in balance.

In a cordless telephone having a base station connectable to a switched telephone network and at least one handset, said base station and handset communicating over a radio frequency link utilizing time division duplex direct sequence quadrature modulation a gain imbalance compensation circuit in said handset and in said base station, each connected to receive the digital in-phase and quadrature baseband signals received over the radio frequency link, the gain imbalance compensation circuit comprising:

• a circuit for introducing a frequency offset signal into the in-phase and quadrature signal channels during the time the handset is in the cradle of the base station;
• a fist digital circuit for detecting a gain imbalance between the resulting signals in the in-phase and quadrature channels;
• and
• a second digital circuit for increasing or decreasing the gain in the in-phase and quadrature signal channels until the gain in the in-phase and quadrature channels are in balance.

In a communication link having in-phase and quadrature baseband channels, a method for balancing the gain between the in-phase and quadrature baseband channels, the steps of the method comprising:

• introducing a frequency offset signal into the in-phase and quadrature channel at the demodulation end during a time no signals are being demodulated;
• detecting a gain difference between the resulting signals in the in-phase and quadature channels;
• and
• adjusting the gain in the in-phase or quadrature channel, as required, to bring the gain in both channels to about the same level.

A system for balancing the gain between the in-phase and quadrature baseband channels, the system comprising:

• means for introducing a frequency offset signal into the in-phase and quadrature channel at the demodulation end during a time no signals are being demodulated;
• means for detecting a gain difference between the resulting signals in the in-phase and quadature channels;
• and
• means for adjusting the gain in the in-phase or quadrature channel, as required, to bring the gain in both channels to about the same level.