US 5,515,047 A · Converter, offset adjustor, and portable communication terminal unit

Abstract

The number of current sources and switches necessary for a plurality of unit D/A converters using equal reference currents, are drastically reduced to reduce the parasitic capacitance coupled to current output lines, by converting a plurality of digital signals of a predetermined bit, which are divided from an input digital signal, into an analog current unit D/A converters and by converting the analog current in a manner to correspond to the weights of the corresponding input digital signals, thereby to synthesize the currents. The fixed reference digital signal is inputted to the D/A converter for cancelling offsets. The offsets of a plurality of analog output signals in positive and opposite phases obtained by branching the output of the D/A converter are individually detected. After this, the DC offset values of the individual analog outputs are used as offset adjusted negative feedback signals for a desired value. One of them is the digital signal to be fed back to the input portion of the D/A converter whereas the other is the analog signal to be fed to a path portion obtained by branching the output of the D/A converter.

Claims9

Dependent claims

A semiconductor integrated circuit device including a first circuit for outputting a digital signal and a second circuit for subjecting first and second analog signals having different phases to a predetermined processing, comprising:

a converter for converting a digital signal into an analog signal;
a branching circuit coupled to the output of said converter for producing said first analog signal and said second analog signal from said analog signal;
a first offset adjustor coupled between said first circuit and said converter for arranging a digital signal to be fed to said converter, in accordance with an adjusting digital signal for adjusting the offset of said first analog signal from said digital signal;
and
a second offset adjustor coupled between said branching circuit and said second circuit for arranging said second analog signal to be fed to said second circuit, in accordance with an adjusting analog signal for adjusting the offset of said second analog signal from said digital signal.

2 more elements

A semiconductor integrated circuit device including a D/A converter, comprising:

an offset adjustor for adjusting the offsets of a plurality of analog signals obtained by branching the output of said D/A converter and having different phases,
wherein said offset adjustor generates a plurality of offset adjusting negative feedback signals, of which at least one is a digital signal to be negatively fed back to a path at the input side of said D/A converter whereas the others are analog signals to be negatively fed back to systems branched midway from the system which has its offset adjusted by the offset adjusting negative feedback signal or said digital signal.

Dependencies are inferred from the claim text.

Converter, offset adjustor, and portable communication terminal unit

Life of this patent

Converter, offset adjustor, and portable communication terminal unit

Life of this patent

Abstract

Claims9