US 5,589,847 A · Switched capacitor analog circuits using polysilicon thin film technology

Abstract

Switched capacitor analog circuits (such as integrators, amplifiers and digital-to-analog converters) constructed from polysilicon thin film transistors and capacitors are disclosed. The circuits are commonly implemented using conventional single crystal CMOS technologies, but this is the first time they have been realized using polysilicon TFT CMOS. The performance of the circuits is inevitably worse than that of conventional single crystal CMOS devices, but is nevertheless adequate for many large area applications. The circuits can be fabricated on large area substrates and integrated with, for example, flat panel displays, pagewidth optical scan arrays, or pagewidth printheads, offering improvements in the functionality and performance of those devices. Charge redistribution amplifiers and digital-to-analog converters are shown to operate with settling times ranging from a few microseconds to a few tens of microseconds, even with large capacitive loads, despite the relatively poor performance of polysilicon TFTs in comparison to conventional MOSFETS. Better than 8-bit accuracy is also demonstrated for the digital-to-analog converters.

Claims27

Dependent claims

An analog switched capacitor circuit comprising:

at least one polysilicon thin film capacitor means;
at least one polysilicon thin film transistor switch means;
at least one polysilicon thin film amplifier means;
and
interconnection means for interconnecting the capacitor means, the transistor switch means, and the amplifier means so that the output of said circuit is set by the accumulation of electrical charge on said capacitor means under the control of said transistor switch means and said amplifier means;
said capacitor means, said transistor switch means, said amplifier means, and said interconnection means all being formed on a common substrate.

3 more elements

An analog switched capacitor circuit comprising:

an amplifier constructed from polysilicon thin film transistors and having an input and an output;
a polysilicon thin film input capacitor having an output attached to said amplifier input;
a first polysilicon thin film transistor attached to an input of said input capacitor, for selectively attaching said input capacitor to an input voltage source based upon a first control signal;
a second polysilicon thin film transistor attached to said input of said input capacitor, for selectively attaching said input capacitor to ground based upon a second control signal;
a polysilicon thin film feedback capacitor attached between said output and said input of said amplifier;
a third thin film polysilicon transistor attached between said output and said input of said amplifier, for selectively discharging said feedback capacitor based upon one of said first and second control signals;
wherein a capacitance of said input and said feedback capacitors is chosen, and said first, second and third transistors are controlled so that the output of said circuit is set by the transfer and distribution of charge among said input and feedback capacitors under the control of said first, second and third transistors;
and
said amplifier, said input and feedback capacitors, and said first, second and third transistors all being formed on a common substrate.

6 more elements

Dependencies are inferred from the claim text.

Switched capacitor analog circuits using polysilicon thin film technology

Life of this patent

Switched capacitor analog circuits using polysilicon thin film technology

Life of this patent

Abstract

Claims27