Direct-conversion transmitting circuit and integrated transmitting/receiving circuit

Abstract

A transmitter is provided which includes a transmitting circuit that does not require a high-performance low noise VCO restricting cost reduction thereof and that can reduce the number of parts without requiring an RF filter. A direct conversion that does not require a transmission VCO is applied to the transmitting circuit. In order to achieve noise reduction in a receiving band, low-pass filters are provided at IQ input sections of a modulator that converts IQ signals into RF signals. In comparison with a conventional transmitter using offset PLL, an external VCO required in addition to an RF integrated circuit, a power amplifier, and a front end circuit is reduced. Even in current transistor performance, by using a filter having rapid waveform characteristics such as a SAW more inexpensive than the VCO, or the like, it is possible to provide a GSM/GSM 1800/GSM1900 triple band transmitter.

1 . A direct-conversion transmitting circuit comprising: 
 a modulator to modulate I and Q signals into a transmitting frequency signal, the I and Q signals being inputted from a base band circuit to said modulator;    a first driver amplification circuit coupled to an output node of said modulator to amplify a first transmitting frequency signal being modulated into a first frequency band through said modulator;    a second driver amplification circuit coupled to an output node of said modulator to amplify a second transmitting frequency signal being modulated into a second frequency band through said modulator, the second frequency band being higher than the first frequency band;    first and second low-pass filters being coupled at output nodes thereof to input nodes of said modulator;    first and second gain/bias adjusters being coupled at output nodes thereof to input nodes of said first and second low-pass filters, respectively; and    wherein said modulator comprises first and second mixers, and a first phase shifter,    wherein high frequency output terminals of said first and second mixers are connected to each other,    wherein an output terminal of said first low-pass filter is connected to an input terminal of said first mixer, and an input terminal of said first low-pass filter is connected to an output terminal of said first gain/bias adjuster to suppress a noise generated by said first gain/bias adjuster,    wherein an output terminal of said second low-pass filter is connected to an input terminal of said second mixer, and an input terminal of said second low-pass filter is connected to an output terminal of said second gain/bias adjuster to suppress a noise generated by said second gain/bias adjuster,    wherein a first output terminal of said first phase shifter is connected to a local signal input terminal of said first mixer, and a second output terminal of said first phase shifter is connected to a local signal input terminal of said second mixer,    wherein an input signal generated from an output signal of a first AD converter is applied to an input terminal of said first gain/bias adjuster to reduce difference in gain and bias levels between an input signal of said first mixer and an output signal of said first AD converter, and    wherein an input signal generated from an output signal of a second AD converter is applied to an input terminal of said second gain/bias adjuster to reduce difference in gain and bias levels between an input signal of said second mixer and an output signal of said second AD converter.    
   
   
       2 . The direct-conversion transmitting circuit according to  claim 1 , wherein said first phase shifter is comprised of a frequency divider circuit.  
   
   
       3 . The direct-conversion transmitting circuit according to  claim 1 , wherein each circuit of said first and second low-pass filters is comprised of a filter whose order is at least a second order.