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D/A conversion circuit having n switches, n capacitors and a coupling capacitor
| Details |
Inventors: Tanaka, Yukio;
Assignee: Semiconductor Energy Laboratory Co., Ltd. (JP)
Primary Examiner: Tokar; Michael
Assistant Examiner: Mai; Lam T.
Attorney, Agent or Firm: Cook, Alex, McFarron, Manzo, Cummings & Mehler, Ltd.
A D/A conversion circuit is described which comprises a n switching, n capacitors and a coupling circuit. Upper n bit of the digital signal control n switches respectively and control charging and discharging of electric charge into the n capacitors, and the n capacitors are connected to the output line in an upper bit writing period. Lower n bit of the digital signal control the n switches and control charging and discharging of electric charge into the n capacitors, and the capacitors are connected to the output line through the coupling capacitor in a lower bit writing period. |
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DETAILED DESCRIPTION The present invention has been made in view of the above problems, and has an object to provide a D/A conversion circuit which can make its area small.
The DAC of the invention will be described below.
The present invention relates to a DAC for converting a 2n-bit digital signal into an analog signal, and is characterized in that the 2n-bit digital signal is divided into upper n bits and lower n bits, and after the upper n bits are inputted to the DAC, the lower n bits are inputted to the DAC.
When the digital signal of the upper n bits is inputted to the DAC, one electrode of each of n capacitors with capacitance value expressed by 2.
sup.
n-1 C (C is a constant) is connected to a power source L or a power source H.
A potential V.
sub.
out1 of an analog signal by upper bit information is given from the DAC to a source signal line connected to the other electrode of each of the n capacitors.
Subsequently, the digital signal of the lower n bits is inputted to the DAC, so that the one electrode of each of the n capacitors is connected to the power source L or the power source H.
A potential V.
sub.
out2 of an analog signal by the lower bit information from the DAC is given to the source signal line connected to the other electrode of each of the n capacitors through a coupling capacitor C.
sub.
k having a constant capacitance value.
Like this, after the analog signal by the upper bit information is written to the source signal line, the analog signal by the lower bit information is further written, so that the analog signal by the upper bit information is combined with the analog signal by the lower bit information to form an analog signal and it can be inputted to the source signal line.
The capacitance value of the coupling capacitor C.
sub.
k can be suitably set by a designer so that the analog signal outputted from the DAC is linearly changed by changing bit information of the digital signal.
Since the present invention has the foregoing structure, it has become possible to convert the 2n-bit digital signal into the analog signal by the DAC using the n capacitors and one coupling capacitor C
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