Bias drive and noise reduction in image projectors

A bias drive circuit for use in an image projector, said bias drive circuit comprising:

• an amplifier having first and second inputs and an output, and wherein the first input of the amplifier is adapted to receive a square wave input signal;
• a feedback network coupled between the output and the second input of the amplifier that is adapted to feed back output signals provided by the bias drive circuit to the amplifier and modify the output signal therefrom such that its output waveform, when applied to the image projector, results in a square wave applied thereto;
• and
• a frequency synthesizer comprising:
• a divide by two divider having an input adapted to receive an input frequency signal;
• a phase detector having a first input coupled to an output of the divide by two divider;
• a filter circuit having an input coupled to an output of the phase detector;
• a voltage controlled oscillator having an input coupled to an output of the filter circuit;
• a second divide by two divider having an input coupled to an output of the voltage controlled oscillator, said second divide by two divider providing an output frequency signal (f.sub.OUT) from the frequency synthesizer by way of an output, said output frequency signal (f.sub.OUT) comprising said square wave input signal received by said amplifier first input;
• and
• a divide by N divider coupled between the output of the second divide by two divider and a second input of the phase detector;
• wherein a divide number of the divide by N divider is an odd number and the input frequency signal is divided by two so that every other field is employed as a reference input to the bias drive circuit.

A bias drive circuit for use in an image projector comprising a liquid crystal light valve including a liquid crystal, said bias drive circuit comprising:

• an amplifier having first and second inputs and an output, and wherein the first input of the amplifier is adapted to receive a square wave input signal;
• a feedback network means coupled between the output and the second input of the amplifier for feeding back output signals provided by the bias drive circuit to the amplifier and for modifying the output signal such that its waveform is a non-square wave that, when applied to the liquid crystal light valve, results in a square wave within the liquid crystal;
• and
• a frequency synthesizer comprising:
• a divide by two divider having an input adapted to receive an input frequency signal;
• a phase detector having a first input coupled to an output of the divide by two divider;
• a filter circuit having an input coupled to an output of the phase detector;
• a voltage controlled oscillator having an input coupled to an output of the filter circuit;
• a second divide by two divider having an input coupled to an output of the voltage controlled oscillator, said second divide by two divider providing an output frequency signal (f.sub.OUT) from the frequency synthesizer by way of an output, said output frequency signal (f.sub.OUT) comprising said square wave input signal received by said amplifier first input;
• and
• a divide by N divider coupled between the output of the second divide by two divider and a second input of the phase detector.

A bias drive circuit for use in an image projector comprising a liquid crystal light valve including a liquid crystal, said bias drive circuit comprising:

• an amplifier having first and second inputs and an output, and wherein the first input of the amplifier is adapted to receive a square wave input signal;
• a feedback network coupled between the output and the second input of the amplifier that is adapted to feed back output signals provided by the bias drive circuit to the amplifier and modify the output signal such that its waveform, when applied to the liquid crystal light valve, results in a square wave applied to the liquid crystal thereof;
• and
• a frequency synthesizer comprising:
• a divide by two divider having an input adapted to receive an input frequency signal;
• a phase detector having a first input coupled to an output of the divide by two divider;
• a filter circuit having an input coupled to an output of the phase detector;
• a voltage controlled oscillator having an input coupled to an output of the filter circuit;
• a second divide by two divider having an input coupled to an output of the voltage controlled oscillator, said second divide by two divider providing an output frequency signal (f.sub.OUT) from the frequency synthesizer by way of an output, said output frequency signal (f.sub.OUT) comprising said square wave input signal received by said amplifier first input;
• a divide by N divider coupled between the output of the second divide by two divider and a second input of the phase detector;
• and
• wherein a divide number of the divide by N divider is an odd number and the input frequency signal is divided by two so that every other field is employed as a reference input to the bias drive circuit.

A bias drive circuit for use in an image projector comprising a liquid crystal light valve including a liquid crystal, said bias drive circuit comprising:

• an amplifier having first and second inputs and an output, and wherein the first input of the amplifier is adapted to receive a square wave input signal;
• a feedback network coupled between the output and the second input of the amplifier that is adapted to feed back output signals provided by the bias drive circuit to the amplifier and modify the output signal such that its waveform, when applied to the liquid crystal light valve, results in a square wave applied to the liquid crystal thereof;
• and
• a frequency synthesizer comprising:
• a divide by two divider having an input adapted to receive an input frequency signal;
• a phase detector having a first input coupled to an output of the divide by two divider;
• a filter circuit having an input coupled to an output of the phase detector;
• a voltage controlled oscillator having an input coupled to an output of the filter circuit;
• a second divide by two divider having an input coupled to an output of the voltage controlled oscillator, said second divide by two divider providing an output frequency signal (f.sub.OUT) from the frequency synthesizer by way of an output, said output frequency signal (f.sub.OUT) comprising said square wave input signal received by said amplifier first input;
• a divide by N divider coupled between the output of the second divide by two divider and a second input of the phase detector;
• and
• a variable gain circuit that is adapted to set the amplitude of the bias provided by the bias drive circuit to a cut-in operating point of the liquid crystal light valve.

Apparatus for driving a liquid crystal light valve including a liquid crystal, which liquid crystal light valve forms part of an image projector, said apparatus comprising:

• a frequency synthesizer comprising:
• a divide by two divider having an input adapted to receive an input frequency signal;
• a phase detector having a first input coupled to an output of the divide by two divider;
• a filter circuit having an input coupled to an output of the phase detector;
• a voltage controlled oscillator having an input coupled to an output of the filter circuit;
• a second divide by two divider having an input coupled to an output of the voltage controlled oscillator, said second divide by two divider providing an output frequency signal (f.sub.OUT) from the frequency synthesizer by way of an output;
• a divide by N divider coupled between the output of the second divide by two divider and a second input of the phase detector;
• and
• a bias drive circuit coupled to the frequency synthesizer that comprises:
• an amplifier having first and second inputs and an output;
• wherein the first input of the amplifier is adapted to receive a square wave input signal comprising said frequency synthesizer output frequency signal (f.sub.OUT);
• and
• a feedback network means coupled between the output and the second input of the amplifier, for feeding back output signals provided by the bias drive circuit to the amplifier and for modifying the output signal such that its output waveform is a non-square wave that, when applied to the liquid crystal, results in a square wave applied within.

The apparatus for driving a liquid crystal light valve including a liquid crystal, which liquid crystal light valve forms part of an image projector, said apparatus comprising:

• a frequency synthesizer comprising:
• a divide by two divider having an input adapted to receive an input frequency signal;
• a phase detector having a first input coupled to an output of the divide by two divider;
• a filter circuit having an input coupled to an output of the phase detector;
• a voltage controlled oscillator having an input coupled to an output of the filter circuit;
• a second divide by two divider having an input coupled to an output of the voltage controlled oscillator, said second divide by two divider providing an output frequency signal (f.sub.OUT) from the frequency synthesizer by
• a divide by N divider coupled between the output of the second divide by two divider and a second input of the phase detector;
• a bias drive circuit coupled to the frequency synthesizer that comprises:
• an amplifier having first and second inputs and an output;
• wherein the first input of the amplifier is adapted to receive a square wave input signal comprising said frequency synthesizer output frequency signal (f.sub.OUT);
• and
• a feedback network coupled between the output and the second input of the amplifier, that is adapted to feed back output signals provided by the bias drive circuit to the amplifier and modify the output signal such that its waveform, when applied to the liquid crystal, results in a square wave applied thereto;
• and
• wherein a divided number of the divide by N divider is an odd number and the input frequency signal is divided by two so that every other field is employed as a reference input to the bias drive circuit.

Apparatus for driving a liquid crystal light valve including a liquid crystal, which liquid crystal light valve forms part of an image projector, said apparatus comprising:

• a frequency synthesizer comprising:
• a divide by two divider having an input adapted to receive an input frequency signal;
• a phase detector having a first input coupled to an output of the divide by two divider;
• a filter circuit having an input coupled to an output of the phase detector;
• a voltage controlled oscillator having an input coupled to an output of the filter circuit;
• a second divide by two divider having an input coupled to an output of the voltage controlled oscillator, said second divide by two divider providing an output frequency signal (f.sub.OUT) from the frequency synthesizer by way of an output;
• a divide by N divider coupled between the output of the second divide by two divider and a second input of the phase detector;
• and
• a bias drive circuit coupled to the frequency synthesizer that comprises:
• an amplifier having first and second inputs and an output;
• wherein the first input of the amplifier is adapted to receive a square wave input signal comprising said frequency synthesizer output frequency signal (f.sub.OUT);
• and
• a feedback network coupled between the output and the second input of the amplifier, that is adapted to feed back output signals provided by the bias drive circuit to the amplifier and modify the output signal such that its waveform, when applied to the liquid crystal, results in a square wave applied thereto;
• and
• further comprising a variable gain circuit that is adapted to set the amplitude of the bias provided by the bias drive circuit to a cut-in operating point of the liquid crystal light valve.