Adaptable current mirror

• US 5,073,759 A
• Filed: 10/31/1990
• Issued: 12/17/1991
• Est. Priority Date: 12/09/1988
• Status: Expired due to Term

• Current Assignee: Synaptics Incorporated
• Original Assignee: Synaptics Incorporated
• Inventors: Allen, Timothy P., Mead, Carver A.
• Primary Examiner(s): MOTTOLA, STEVEN J
• Application Number:
  US07/607,141
• Time in Patent Office: 412 Days
• Field of Search: 330/277, 330/288, 330/308, 330/9, 307/296.6, 323/315, 323/316
• US Class Current: 330/288
• CPC Class Codes: G06N 3/063 using electronic means
• CPC Class Codes: H01L 27/0629 in combination with diodes, or resistors, or capacitors
• CPC Class Codes: H03F 1/0261 with control of the polarisation voltage or current, e.g. gliding Class A
• CPC Class Codes: H03F 1/303 using a switching device H03F1/305, H03F3/005, H03F3/38 take precedence
• CPC Class Codes: H03F 3/45479 characterised by the way of common mode signal rejection
• CPC Class Codes: H03F 3/45753 using switching means, e.g. sample and hold
• CPC Class Codes: H03F 3/45977 using switching means, e.g. sample and hold

Abstract

An integrated circuit amplifier having a random input offset voltage is adaptable such that then input offset voltage may be cancelled out. An inverting input node is a floating input node and is coupled to a source of input signal by a first capacitor. A second capacitor is connected between the output of the amplifier and the floating node. An ultraviolet window above the second capacitor allows the floating node to be charged, by the application of ultraviolet light, to a voltage which effectively cancels the input offset voltage. The ultraviolet window and capacitor electrodes are arranged such that the ultraviolet light may strike only the desired areas of the structure.

Claims

1. An adaptable current mirror having an input node and an output node, including:

first and second MOS transistors, each having a source, a gate, and a drain,

first and second MOS capacitors, each having first and second electrodes,

the source of said first MOS transistor being connected to a source of fixed voltage, the gate and drain of said first MOS transistor being connected to said input node and to said first electrode of said first capacitor, the source of said second MOS transistor being connected to a source of fixed voltage, the gate of said second MOS transistor being connected to said second electrode of said first capacitor and to said first electrode of said second capacitor, the drain of said second MOS transistor forming said output node and being connected to said second electrode of said second capacitor,

means for supplying a calibration current to said input node during adaptation,

means for selectively supplying a desired output current to said output node during adaptation,

means for selectively illuminating said first and second electrodes of said second capacitor with ultraviolet light during adaptation,

whereby the output current of said current mirror is adapted to be equal to said desired output current when its input current is equal to said calibration current.

2. An adaptable current mirror having an input node and an output node, including:

first and second MOS transistors, each having a source, a gate, and a drain,

first and second MOS capacitors, each having first and second electrodes,

the source of said first MOS transistor being connected to a source of fixed voltage, the gate and drain of said first MOS transistor being connected to said input node and to said first electrode of said first capacitor, the source of said second MOS transistor being connected to a source of fixed voltage, the gate of said second MOS transistor being connected to said second electrode of said first capacitor and to said first electrode of said second capacitor, the drain of said second MOS transistor forming said output node and being selectively connected to said second electrode of said second capacitor,

means for supplying a calibration current to said input node during adaptation,

means for selectively supplying a desired output current to said output node during adaptation,

means for selectively illuminating said first and second electrodes of said second capacitor with ultraviolet light during adaptation,

whereby the output current of said current mirror is adapted to be equal to said desired output current when its input current is equal to said calibration current.

3. The adaptable current mirror of claim 2 further including means for selectively connecting said first electrode of said second capacitor to said output node during adaptation and to a source of fixed voltage during normal operation.