1. Field
The present invention relates to a digital/analog (D/A) converter that converts a digital signal to an analog signal.
2. Description of the Related Art
In a signal processing in radio communication, the amplitude and phase of a signal are operated and thus there is often used a two-dimensional orthogonal signal of In-phase/Quadrature-phase (I/Q). Therefore, as disclosed in Porra, V., Halonen, K., Koli, K., Paakonen, M., Siilasto, S., Tiiliharju, E., Tolonen, P. and Wahlroos, T., “Low voltage circuits for a single chip 2 GHz transceiver for mobile telecommunication”, International Symposium on Circuits and Systems, Vol. 1, pages 492-495 (12-15 May, 1996), a D/A converter in a radio transmitter generally operates two signals of I/Q signals.
Also, to output I/Q analog signals as differential signals respectively, as shown in FIG. 10, generally, a two-phase D/A converter is used for an I signal and another two-phase D/A converter is used for the Q signal. In FIG. 10, the analog value of the I digital signal is obtained by a difference between OUT I+ and OUT I−, while the analog value of a Q digital signal is obtained by a difference between OUT Q+ and OUT Q−.
As in the technique described above, when two differential output type D/A converters are used, conversion accuracies of the two converters do not coincide with each other because of a matching error between the two D/A converters. Also, when there are provided the two independent differential output type D/A converts, the chip area and power consumption thereof unfavorably increase. And, when a load is provided as an external load, the number of parts increases.