Analog-to-digital converter and method of fabrication
First Claim
1. A method of error correction in a two-step analog-to-digital converter, comprising the steps of:
- (a) converting an input analog signal to an N-bit digital word;
(b) reconstructing a second analog signal from said N-bit word;
(c) converting an amplified difference between said input analog signal and said second signal to an M-bit word where the amplification is by a factor of 2K ;
(d) adding to said N-bit word the two'"'"'s complement of the N-K most significant bits of the M-bit word which would result from a conversion of 0 in step (c) and thereby form a second N-bit word plus a first carry bit;
(e) adding to said second N-bit word the N-K most significant bits of said M-bit word to form a third N-bit word plus a second carry bit; and
(f) forming an output digital word with its N most significant bits equal to said third N-bit word and its M-(N-K) least significant bits equal to the M-(N-K) least significant bits of said M-bit word.
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Abstract
A two-step analog-to-digital converter and BiCMOS fabrication method. The fabrication method provides pseudosubstrate isolation of digital CMOS devices from the analog devices. The converter uses NPN current switching in a flash analog-to-digital converter and in a digital-to-analog converter for low noise operation. CMOS digital error correction and BiCMOS output drivers provide high packing density plus large output load handling. Timing control aggregates switching events and puts them into intervals when noise sensitive operations are inactive. The fabrication method uses a thin epitaxial layer with limited thermal processing to provide NPN and PNP devices with large breakdown and Early voltages. Laser trimmed resistors provide small long term drift due to dopant stabilization in underlying BPSG and low hydrogen nitride passivation.
34 Citations
15 Claims
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1. A method of error correction in a two-step analog-to-digital converter, comprising the steps of:
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(a) converting an input analog signal to an N-bit digital word; (b) reconstructing a second analog signal from said N-bit word; (c) converting an amplified difference between said input analog signal and said second signal to an M-bit word where the amplification is by a factor of 2K ; (d) adding to said N-bit word the two'"'"'s complement of the N-K most significant bits of the M-bit word which would result from a conversion of 0 in step (c) and thereby form a second N-bit word plus a first carry bit; (e) adding to said second N-bit word the N-K most significant bits of said M-bit word to form a third N-bit word plus a second carry bit; and (f) forming an output digital word with its N most significant bits equal to said third N-bit word and its M-(N-K) least significant bits equal to the M-(N-K) least significant bits of said M-bit word. - View Dependent Claims (2, 3, 4)
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5. An integrated circuit two-step analog-to-digital converter, comprising:
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(a) an analog-to-digital converter (ADC) having an input and output; (b) a digital-to-analog converter (DAC) with an input switchably coupled to either the output of said ADC or to a fixed bit pattern; (c) an error amplifier with an input coupled to the output of said DAC and an output selectively connectable to the input of the ADC; (d) A controller, said controller holding said error amplifier inactive for a first time interval immediately following a switching of the input of said DAC from said fixed bit pattern to said output of said ADC. - View Dependent Claims (6, 7, 8, 9)
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10. A two-step analog-to-digital converter, comprising:
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(a) an N-bit analog-to-digital converter (ADC) coupled to a sample terminal; (b) an N-bit digital-to-analog converter (DAC) coupled to the output of said N-bit ADC; (c) an error amplifier with inputs coupled to the sample terminal and an output of the DAC for amplifying the difference between a signal at said sample terminal and the output of said DAC, said amplifier amplifying by a factor of 2K where K is less than N; (d) an M-bit ADC coupled to an output of said error amplifier; (e) error correction circuitry coupled to the outputs of said N-bit and M-bit ADCs and including; (i) an adder which adds to an N-bit word output of said N-bit ADC the two'"'"'s complement of the N-K most significant bits of the M-bit word which would result from a conversion of 0 by M-bit ADC to form a second N-bit word, (ii) a second adder which adds the N-K most significant bits of an M-bit word output of said M-bit ADC to said second N-bit word outputs by said adder, (f) output circuitry coupled to the output of said error correction circuitry and the output of said M-bit ADC, said output circuitry concatenating an N-bit output of said second adder with the M-N+K least significant bits of an output of said M-bit ADC. - View Dependent Claims (11, 12)
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13. A method of two-step analog-to-digital conversion, comprising the steps of:
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(a) converting an analog input to a first digital output with a first analog-to-digital converter (ADC) while a digital-to-analog converter (DAC) has a fixed input and an error amplifier with input coupled to the output of said DAC is clamped to a fixed output; (b) switching the input of said DAC from said fixed input to the output of said first ADC while said error amplifier remains clamped; (c) unclamping said error amplifier after waiting a first time interval from said switching the input of said DAC; (d) converting the output of said error amplifier with a second ADC; and (e) combining the results of said conversions in said first ADC and second ADC. - View Dependent Claims (14, 15)
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Specification