Slew rate controlled ramp and its use in liquid crystal displays
First Claim
1. A ramp source, comprising:
- an operational transconductance amplifier (OTA) having an inverting input, a non-inverting input, an output, and a tail current line;
a load connected to said output;
a first current source for sinking a first current from said tail current line;
a switch having a first terminal connected to said tail current line, a second terminal, and a switch control, wherein said first terminal and said second terminal are electrically shorted together when said switch control receives a close signal; and
a second current source connected to said second terminal;
wherein said second current source is for sinking a second current from said tail current line when said switch control receives said close signal.
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Accused Products
Abstract
An operational transconductance amplifier (OTA) circuit, and a liquid crystal display that uses such an OTA circuit, having a controlled slew rate. The OTA has an output that drives a load, beneficially a liquid crystal display panel. That OTA includes a first current source that sinks a first tail current, and a second current source that selectively sinks a second tail current. That second current source is selected by a control signal applied to a switch. When the second current source sinks the additional second tail current the slew rate of the OTA is increased. When used in a liquid crystal display, the OTA drives the liquid crystal display panel with a ramp. During ramp fly back, the second current source sinks the second tail current and increases the slew rate.
11 Citations
20 Claims
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1. A ramp source, comprising:
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an operational transconductance amplifier (OTA) having an inverting input, a non-inverting input, an output, and a tail current line;
a load connected to said output;
a first current source for sinking a first current from said tail current line;
a switch having a first terminal connected to said tail current line, a second terminal, and a switch control, wherein said first terminal and said second terminal are electrically shorted together when said switch control receives a close signal; and
a second current source connected to said second terminal;
wherein said second current source is for sinking a second current from said tail current line when said switch control receives said close signal. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. A liquid crystal display, comprising:
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a plurality of pixel elements in an array of pixel rows and pixel columns, wherein each pixel element includes a ramp input line;
a ramp generator producing a ramp during a ramp period and a return during a fly back period;
an operational transconductance amplifier (OTA) having a non-inverting input connected to said ramp generator, an inverting input, an output connected to said pixel element ramp input lines and to said inverting input, and a tail current line;
a first current source for sinking a first current from said tail current line;
a switch having a first terminal that is connected to said tail current line, a second terminal, and a switch control, wherein said first terminal and said second terminal are electrically shorted together when said switch control is closed; and
a second current source connected to said second terminal, said second current source for sinking a second current from said tail current line when said switch control is closed; and
a control for closing said switch control during said fly back period. - View Dependent Claims (9, 10, 11, 12, 13, 14, 15, 16, 17, 18)
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19. An operational transconductance amplifier circuit, comprising:
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an operational transconductance amplifier (OTA) having an inverting input, a non-inverting input, an output, and a tail current line;
a load connected to said output;
a first current source for sinking a first current from said tail current line;
a switch having a first terminal connected to said tail current line, a second terminal, and a switch control, wherein said first terminal and said second terminal are electrically shorted together when said switch control receives a close signal; and
a second current source connected to said second terminal;
wherein said second current source is for sinking a second current from said tail current line when said switch control receives said close signal. - View Dependent Claims (20)
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Specification