| US 7,602,326 B2 | ||
| Digital-to-analog converter having resistor string with ranges to reduce circuit elements | ||
| Shiming Lan, Tokyo (Japan) | ||
| Assigned to Oki Semiconductor Co., Ltd., Tokyo (Japan) | ||
| Filed on Mar. 12, 2008, as Appl. No. 12/46,514. | ||
| Application 12/046514 is a continuation in part of application No. 11/640859, filed on Dec. 19, 2006, granted, now 7,365,670. | ||
| Claims priority of application No. 2006-012327 (JP), filed on Jan. 20, 2006. | ||
| Prior Publication US 2008/0180295 A1, Jul. 31, 2008 | ||
| Int. Cl. H03M 1/66 (2006.01) | ||
| U.S. Cl. 341—145 [341/144] | 16 Claims |
| 1. A digital-to-analog converter for converting a digital input signal to an analog output voltage, comprising:
a first resistor string for generating a series of voltages spanning an upper range, a lower range, and a midrange disposed
between the upper range and the lower range;
a lower selector for selecting one of the voltages in the lower range as the analog output voltage when the digital input
signal has a value equal to or less than a first boundary value;
an upper selector for selecting one of the voltages in the upper range as the analog output voltage when the digital input
signal has a value equal to or greater than a second boundary value;
a pair of midrange selectors for selecting a mutually adjacent pair of voltages in the midrange when the digital input signal
has a value between the first and second boundary values;
a midrange voltage generator for generating a further series of voltages between the pair of voltages selected by the pair
of midrange selectors; and
an output selector for selecting one of the voltages in the further series of voltages as the analog output voltage when the
digital input signal has a value strictly between the first and second boundary values,
wherein the resistor string comprises
a first sub-string of first resistors for generating the voltages in the upper range,
a second sub-string of second resistors for generating the voltages in the midrange, and
a third sub-string of third resistors for generating the voltages in the lower range,
wherein the second sub-string being connected in series between the first sub-string and the third sub-string,
the further series of voltages consists of a number N of voltages, and
the first resistors and the third resistors have larger resistance values than the resistance values of the second resistors
divided by the number N.
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