Time division multiple access time division duplex type

Abstract

A transmitter-receiver of the TDMA/TDD type which includes a phase control loop controlled in such a manner that the loop is turned on during the time slot just preceding each of a transmission time slot and a reception time slot, and the loop is turned off during all other time periods including the transmission time slot and the reception time slot. The voltage controlled oscillator includes a variable capacitance diode which produces an output frequency in response to a frequency control voltage received from a charge pump when the loop is closed, and in response to a charging voltage supplied from a loop filter when the loop is open. When the loop is closed, a phase comparator compares a reference frequency signal with an output frequency signal of the voltage-controlled oscillator and generates error signals for controlling the charge pump. A state switching unit switches the state of the phase comparator between an operating state, when the loop is closed, and a stand-by state in response to a power saving signal when the loop is open. A bias supply unit applies a variable bias voltage to an anode of the variable capacitance diode. The variable bias voltage varies in nearly the same manner as the charging voltage supplied to a cathode of the variable capacitance diode from the loop filter when the phase comparator is in a stand-by state, thereby maintaining the voltage across the variable capacitance diode at a relatively constant level such that the output frequency signal is maintained at a desired level.