Abstract: When the radio circuit apparatus is transmitting, the output signal of the first local oscillator 102 is inputted to the transmitted frequency converter 112 as well as to the frequency divider 104, and then the output signal of the frequency divider 104 is inputted to the modulator 111. The modulator 111 modulates the output signal of the frequency divider 104 with a base band signal. The output signal of the modulator 111 is inputted to the transmitted frequency converter 112, to be converted to the frequency of a transmitted signal by the output signal of the first local oscillator 102. When the radio circuit apparatus is receiving, the output signal of the low noise amplifier 121 is inputted to the first frequency converter 122 to be converted to the first intermediate frequency by the output signal of the first local oscillator 102.

Abstract: A power amplifier has an input signal splitting part for splitting the input signal into two output signals each having equal power and phase difference of 180 degrees with respect to each other. A first signal on-off selection part for switching conduction of one of the output signals. A first amplifying part for amplifying the signal from the first signal on-off selection part. A second signal on-off selection part for switching conduction of the signal outputted from the first amplifying part. A second amplifying part for amplifying the other of the output signals from the input signal splitting part. An output signal combining part for providing a phase difference of 180 degrees between the output of the second signal on-off selection part and the output of the second amplifying part and combining them.

Abstract: Disclosed is a transmitter for switching and transmitting signals of plural frequency bands. For example, the signals of two frequency bands are switched and transmitted. For the transmission in a first frequency band, of transistors 104, 105 are turned off, whereby a power amplifying transistor 102 is matched by an input wide band matching circuit 101 and an output main matching circuit 103, so that the high efficiency linear amplification is accomplished. For the transmission in a second frequency band, the transistor 104 is turned on while the transistor 105 is turned off, whereby the power amplifying transistor 102 is matched by a capacitance 108 as well as the input wide band matching circuit 101 and the output main matching circuit 103, so that the high efficiency linear amplification is accomplished. An external switch for switching the matching circuits is thus unnecessary.

Abstract: A transceiver circuit with a heterodyne receiver circuit is provided. Output signals of first and second local oscillator 103, 104 are mixed by a local frequency converter 105. An output signal of the converter 105 passes a filter 106 and inputs a modulator 111 of a transmitter circuit 101 as well as a first frequency converter 122 of a receiver circuit 102. The second local oscillator 104 comprises a frequency synthesizer whose output signal varies for a transmission or a receiving mode. The output signal of the second local oscillator 104 also inputs the second frequency converter 124 of the receiving mode. A reference frequency of the second local oscillator 104 is set higher than a frequency step between communication channels so that a quick switching of the frequency is performed. Thus, the transceiver circuit of this invention is suitable for a compact size and hardly generates unwanted spurious components at transmission mode.

Abstract: A frequency synthesizer that can switch an output frequency fast and generates little spurious output is provided. This frequency synthesizer comprises a phase locked loop including a voltage-controlled oscillator, a high frequency divider, a phase frequency comparator and a low-pass filter. The divisor controller circuit supplies a divisor that varies cyclically to the high frequency divider for a fractional dividing operation. When switching the output frequency, a passing bandwidth of the low-pass filter is enlarged to widen a loop bandwidth of the phase locking loop for fast switching. After switching, the passing bandwidth of the low-pass filter is reduced to narrow the loop bandwidth for reduction of a spurious output, at the timing when a predetermined period has passed for the switched output frequency to stabilize substantially.

Abstract: An antenna switching device of the present invention includes: a transmitting terminal for receiving a transmitting signal; a first antenna terminal connected to a first antenna; a second antenna terminal connected to a second antenna; a receiving terminal for outputting receiving signals received at the first antenna terminal and the second antenna terminal; a selecting unit for selecting one mode among a first mode for outputting a signal corresponding to the transmitting signal to the first antenna terminal, a second mode for outputting the receiving signal received at the first antenna to the receiving terminal, and a third mode for outputting the receiving signal received at the second antenna to the receiving terminal.