DIGITAL RADIO TRANSMITTER
There is provided a digital radio transmitter capable of meeting a legal standard even if unwanted emissions resulting from a switching frequency of a switching power supply occur in transmission waves. The digital radio transmitter includes: a switching power supply that determines a switching frequency by a synchronization signal of an oscillator; a data readout/transfer circuit that determines a transfer timing frequency of baseband data based on the synchronization signal of the oscillator; and a power amplifier using, as a VCC power source, voltage output from the switching power supply.
1 . A digital radio transmitter comprising:
an oscillator;
a switching power supply that deter mines a switching frequency by a synchronization signal of the oscillator;
a data readout/transfer circuit that determines a transfer timing frequency of baseband data based on the synchronization signal of the oscillator; and
a power amplifier using, as a VCC power source, voltage output from the switching power supply.
2 . The digital radio transmitter according to claim 1 , wherein
a frequency divider is provided between the oscillator and the switching power supply, and
the transfer timing frequency of the baseband data and the switching frequency are frequencies in an integer ratio.
3 . The digital radio transmitter according to claim 1 , wherein
a frequency converter/adder is provided between the data readout/transfer circuit and the power amplifier, and
based on the synchronization signal and a baseband data signal, the frequency converter/adder creates and adds a signal whose phase is opposite in a frequency band identical to that of an unwanted emission.
4 . The digital radio transmitter according to claim 2 , wherein
a frequency converter/adder is provided between the data readout/transfer circuit and the power amplifier, and
based on the synchronization signal and a baseband data signal, the frequency converter/adder creates and adds a signal whose phase is opposite in a frequency band identical to that of an unwanted emission.