Digital/analog conversion device and display device having the same

1. A digital/analog conversion device outputting an analog voltage according to digital data of a plurality of weighted bits, comprising:

a pulse number control circuit supplying, to a first node, pulses of a number according to said digital data, said pulses including a first transition edge changing from an initial level to a predetermined level and a second transition edge returning from said predetermined level to said initial level; and

a charge pump circuit changing, in a stepwise manner, each time one of said pulses is supplied to said first node, a voltage on an output node having an output capacitor connected thereto,

said charge pump circuit including

a pump capacitor connected between a second node and said first node,

a switch element connected between said second node and said output node to be turned on at a timing at which said first transition edge of each of said pulses is transmitted to said first node and turned off at a timing at which said second transition edge thereof is transmitted to said first node and

a bias circuit changing, according to the change of the voltage on said output node, a voltage on said second node with the same polarity as that of the change of the voltage on said output node.

2. The digital/analog conversion device according to claim 1 , wherein

said pulse number control circuit includes

a switch circuit provided between a pulse node to which said pulses are successively supplied and said first node and transmitting, when said switch circuit is turned on, said pulses from said pulse node to said first node and

a switch control circuit turning on said switch circuit for a period of time according to said digital data.

3. The digital/analog conversion device according to claim 1 , further comprising a precharge circuit for setting said first node, said second node and said output node each to a predetermined precharge voltage before said analog voltage is output.

4. The digital/analog conversion device according to claim 3 , wherein

said precharge voltage corresponds to a minimum level in a range over which said analog voltage is controlled, and

said charge pump circuit increases in a stepwise manner the voltage on said output node each time said pulse is transmitted to said first node.

5. The digital/analog conversion device according to claim 3 , wherein

said precharge voltage corresponds to a maximum level in a range over which said analog voltage is controlled, and

said charge pump circuit decreases in a stepwise manner the voltage on said output node each time said pulse is transmitted to said first node.

6. The digital/analog conversion device according to claim 1 , wherein

said bias circuit includes a transistor electrically connected between a power-supply node to which a predetermined voltage is supplied and said second node, and

said transistor has its gate connected to said output node.

7. The digital/analog conversion device according to claim 1 , wherein

said bias circuit includes

a first transistor of a first conductivity type electrically connected between a first power-supply node to which a first predetermined voltage is supplied and said second node,

a current-limiting element connected between a second power-supply node to which a second predetermined voltage is supplied and a third node and

a second transistor of a conductivity type opposite to said first conductivity type connected between a third power-supply node to which a third predetermined voltage is supplied and said third node,

said first transistor has its gate connected to said third node, and

said second transistor has its gate connected to said output node.

8. The digital/analog conversion device according to claim 7 , wherein

said current-limiting element is constituted of a constant-current source supplying a constant current regardless of a voltage difference between said third power-supply node and said third node.

9. The digital/analog conversion device according to claim 1 , wherein

said bias circuit includes

a first transistor of a first conductivity type and a second transistor of a second conductivity type opposite to said first conductivity type that are connected in series between a first power-supply node to which a first predetermined voltage is supplied and said second node,

a current-limiting element connected between a second power-supply node to which a second predetermined voltage is supplied and a third node and

a third transistor of said first conductivity type and a fourth transistor of said second conductivity type connected in series between a third power-supply node to which a third predetermined voltage is supplied and said third node,

said first transistor has its gate connected to said third node,

said fourth transistor has its gate connected to said output node, and

said second and third transistors are each diode-connected.

10. The digital/analog conversion device according to claim 9 , wherein

said current-limiting element is constituted of a constant-current source supplying a constant current regardless of a voltage difference between said third power-supply node and said third node.

11. The digital/analog conversion device according to claim 1 , wherein

said pump capacitor includes a plurality of first adjustment units connected in parallel between said first node and said second node,

said output capacitor includes a plurality of second adjustment units connected in parallel with respect to said output node,

said plurality of first adjustment units and said plurality of second adjustment units each include a unit capacitor and a link element connected in series, and

said link element is configured to be able to select, according to an input from the outside of said first and second adjustment units, whether or not to establish an electrical path including said unit capacitor correlated with said link element.