Analog to digital converter with autoranging offset

• US 5,329,281 A
• Filed: 04/26/1993
• Issued: 07/12/1994
• Est. Priority Date: 04/30/1992
• Status: Expired due to Fees

• Current Assignee: Avago Technologies General IP PTE Limited (Broadcom, Inc.)
• Original Assignee: Hewlett-Packard Company (HP Inc.)
• Inventors: Baumgartner, Richard A., Herleikson, Earl C., Moore, Charles E.
• Primary Examiner(s): Hoff, Marc S.
• Application Number:
  US08/052,859
• Time in Patent Office: 442 Days
• Field of Search: 341/110, 341/118, 341/139, 341/155, 341/172
• US Class Current: 341/139
• CPC Class Codes: A61B 5/30 Input circuits therefor
• CPC Class Codes: A61B 5/305 Common mode rejection
• CPC Class Codes: A61B 5/7203 for noise prevention, reduction or removal
• CPC Class Codes: A61B 5/7242 using integration
• CPC Class Codes: G06G 7/1865 with initial condition setting
• CPC Class Codes: H03F 2200/261 Amplifier which being suitable for instrumentation applications
• CPC Class Codes: H03F 2200/331 Sigma delta modulation being used in an amplifying circuit
• CPC Class Codes: H03F 3/005 using switched capacitors, e.g. dynamic amplifiers; using switched capacitors as resistors in differential amplifiers H03F3/45 takes precedence
• CPC Class Codes: H03F 3/393 with field-effect devices
• CPC Class Codes: H03M 1/005 among different converters types
• CPC Class Codes: H03M 1/181 in feedback mode, i.e. by determining the range to be selected from one or more previous digital output values
• CPC Class Codes: H03M 1/504 using pulse width modulation
• CPC Class Codes: H03M 3/392 Arrangements for selecting among plural operation modes, e.g. for multi-standard operation
• CPC Class Codes: H03M 3/398 among different converter types
• CPC Class Codes: H03M 3/48 characterised by the type of range control, e.g. limiting
• CPC Class Codes: H03M 3/488 using automatic control

Abstract

A mixed analog and digital integrated circuit with features which are especially useful for application as a front end for physiological signal instrumentation such as electrocardiographs, electromyographs, and electroencephalographs. The integrated circuit has 5 signal channels, each with analog amplification and analog to digital conversion. The channels can be configured for various combinations of input signal amplification, input signal summation, analog output driving, and AC impedance measurement. The integrated circuit has 2 digital serial input lines and 2 digital serial output lines, all designed for direct connection to optical couplers. Channel configuration, gain, and other parameters are externally controllable by a serial digital input signal. Up to 6 compatible devices can be serially connected in a chain.

Claims

1. An analog to digital conversion circuit comprising:

summation means for generating a sum of an analog signal input and an analog offset input;

analog to digital converter means, connected to the summation means, for converting the sum to a digital signal output; and

offset means, connected to the digital signal output and receiving a predetermined threshold and a predetermined number, for generating the analog offset input,

wherein the offset means generates the analog offset input if the digital signal output exceeds the predetermined threshold for the predetermined number of consecutive conversions of the analog to digital converter means.

2. An analog to digital conversion circuit as in claim 1 wherein the predetermined threshold further comprises:

an upper threshold,

wherein the offset means generates a negative analog offset input of the digital signal output is greater than the upper threshold for the predetermined number of consecutive conversions of the analog to digital converter means.

3. An analog to digital conversion circuit as in claim 2 wherein the predetermined threshold further comprises:

a lower threshold,

wherein the offset means generates a positive analog offset input if the digital signal output is less than the lower threshold for the predetermined number of consecutive conversions of the analog to digital converter means.

4. An analog to digital conversion circuit as in claim 3 wherein the offset means further comprises:

an offset counter having a digital offset output; and

digital to analog converter means for converting the digital offset output to the analog offset input,

wherein the offset counter is incremented if the digital signal output is greater than the upper threshold for the predetermined number of consecutive conversions of the analog to digital converter means and the offset digital counter is decremented if the digital output is less than the lower threshold for the predetermined number of consecutive conversions of the analog to digital converter means.