Voltage generating circuit with two resistor ladders
View Patent ↗A voltage generating circuit that drives multiple output terminals in alternating positive and negative cycles has two resistor ladders, one resistor ladder generating voltages for the positive cycles, the other resistor ladder generating voltages for the negative cycles. Single-ended amplifiers are connected directly to the resistor ladders, and a switching circuit connects each output terminal to a selectable one of the amplifiers. The output terminals may be precharged to opposite potentials at the beginning of positive and negative cycles, and the resistor ladders may include switching elements that initially set all generated voltages to these potentials so that the amplifiers start each cycle with equal input and output levels, reducing overshoot and undershoot. This voltage generating circuit saves space and power in driving, for example, a display panel in a mobile telephone.
1. A voltage generating circuit comprising:
a first resistor ladder having a plurality of taps for output of respective voltages;
a first plurality of amplifiers with output stages, having respective first input terminals coupled to respective taps in the first resistor ladder;
a second resistor ladder having a plurality of taps for output of respective voltages;
a second plurality of amplifiers with output stages, having respective first input terminals coupled to respective taps in the second resistor ladder;
a plurality of internal signal lines,
a first plurality of switches connected between respective output stages of the first plurality of amplifiers and respective ones of the internal signal lines;
a second plurality of switches connected between respective output stages of the second plurality of amplifiers and respective ones of the internal signal lines;
a plurality of output terminals; and
an output switching circuit connected between the internal signal lines and the output terminals.
2. The voltage generating circuit of claim 1 , wherein the first plurality of amplifiers and the second plurality of amplifiers have respective second input terminals, the second input terminal of each amplifier receiving feedback of the voltage output by the amplifier, the amplifier thus operating as a voltage follower.
3. The voltage generating circuit of claim 1 , wherein the first and second plurality of switches comprise analog switches.
4. The voltage generating circuit of claim 1 , wherein the first resistor ladder has a first end receiving a first potential and a second end receiving a second potential, the second resistor ladder also has a first end receiving the first potential and a second end receiving the second potential, and the first potential is higher than the second potential.
5. The voltage generating circuit of claim 4 , wherein the first resistor ladder comprises resistance elements with a predetermined sequence of resistance values from the first end to the second end, and the second resistor ladder comprises resistance elements with said predetermined sequence of resistance values from the second end to the first end.
6. The voltage generating circuit of claim 1 , further comprising a precharging circuit for precharging the plurality of output terminals to the first potential or the second potential.
7. The voltage generating circuit of claim 4 , wherein the first resistor ladder further comprises a switching element disposed at the second end, for electrically disconnecting the first end from the second end.
8. The voltage generating circuit of claim 4 , wherein the second resistor ladder further comprises a switching element disposed at the first end, for electrically disconnecting the first end from the second end.