Analog Devices,inc.

Charles D Lane

Thomas E Tice

David T Crook

Kevin M Kattmann

John Jerome Kornblum

Ziwei Zheng

Baeton Charles Rigsbee

David C Jarman

Roger B Huntley, Jr

Rodney Louis Kranz

Methods and structures are provided to improve the transfer functions of analog-to-digital converter systems. They address the converter error function that corresponds to a converter's transfer function. In particular, they provide a corrector with a corrector transfer function that defines a corrector error function which substantially mirrors at least a portion of the converter error function. The corrector processes the converter's output digital signals to realize corrector digital signals which are then combined with the original output digital signals to obtain a system with a system error function that is significantly reduced from the original converter error function.

Correction methods and structures for analog-to-digital converter transfer functions

An integrated circuit including a number of repetitive cells for producing output signals in response to respective inputs, each cell having associated with it an output circuit responsive to the cell output signal to produce an output circuit output signal, each of the output circuits including a circuit device having two terminals to provide for the flow therethrough of a current from an associated current supply and producing a corresponding output signal; the improvement for reducing the effects of cell mismatch and output circuit mismatch including an impedance network, having a set of impedance elements each connected between corresponding terminals or respective pairs of the circuit devices with each circuit device forming a part of a respective output circuit, the impedance elements reducing the effects of cell mismatch and output circuit mismatch on the output signals; there maybe one impedance network which accommodates mismatches in both the cells and output circuits or there may be one impedance network to accommodate cell mismatch and another to accommodate output circuit mismatch.

Modified repetitive cell matching technique for integrated circuits

A residue amplifier includes input and output differential amplifiers. The output differential amplifier includes temperature-dependent current sources which compensate for temperature dependent gain variations within the input differential amplifier. Amplifier components are chosen to produce an overall gain equal to a ratio of fixed resistors, at a nominal temperature. The compensating current sources maintain this fixed gain value as the amplifier's operating temperature varies.

Feedforwrd differential amplifier

A new differential ladder/comparator circuit reduces settling time delays in parallel analog to digital converters. A parallel analog-to-digital converter (ADC) includes a pair of differential resistor ladders having their taps connected to a group of comparators. The comparators produce digital 'thermometer' scale outputs corresponding to analog signals impressed upon the differential ladders. By employing double-value resistors to form the 'rungs' of the ladders and by connecting the comparators to the ladder taps in a way that increases the number of comparator inputs connected to the ladders' lower-order taps and decreases the number of comparator inputs connected to the ladders' higher order taps, the input impedance presented by the ladder/comparator combination is reduced in comparison with conventional differential ladder parallel ADCs. Additionally, input signals are superimposed upon the ladders by drivers which, in a preferred embodiment, present lower output impedances to the ladders than prior art drivers, further improving the bandwidth of the ADC.

High bandwidth parallel analog-to-digital converter

A protection circuit inhibits saturation and damage of sensitive circuit elements when an input signal goes out of a nominal input range. The protection circuit includes an out-of-range detector which compares the input signal to reference levels to determine if it is within the range. If it is not, a control circuit substitutes a supplemental signal that is slightly out of range, but not so far out of range as to cause any substantial saturation. Supplemental signal sources that produce supplemental signals slightly outside the high and low ends of the range with error margins, not more than about 750 mV, that lie just outside the range; an out-of-range input is replaced by the supplemental signal with the closest value. The invention is particularly applicable to multistep/subranging analog-to-digital/converters.

High speed saturation prevention for saturable circuit elements

Open-loop differential amplifiers (120, 140) are disclosed which have accurate and stable gain. The gain of these amplifiers is substantially insensitive to the effects of small-signal emitter resistance r.sub.e, current gain .beta. and Early voltage V.sub.A. Thus, their gain can be accurately set by resistance ratios which makes them particularly useful in integrated circuits. These advantages are obtained with an output differential pair (67) that has cross-coupled base and collector terminals. In addition, resistors (141, 143, 148, 150) and a current source (146) associated with this differential pair are related to like elements (27, 28, 24, 25 and 26) that are associated with an input differential pair (21) by disclosed numerical ratios, e.g., the nominal gain G of the amplifier. Versions of the amplifiers can be adapted for use as a residue amplifier (162) in a subranging A/D converter (160).

Differential amplifiers which can form a residue amplifier in

An overvoltage protection circuit protects against saturation and damage of sensitive circuitry elements. The protection circuit includes an out-of-range detector which compares an input signal to reference levels to determine if it is within a predetermined range of acceptable inputs. If the input is determined not to be within this range, a control circuit substitutes a supplemental signal within the range for the input signal. Digital correction can be provided to correct the output of the sensitive circuit element while the supplemental signal is being substituted. Numerous circuit designs may be used to implement the protection scheme.

High speed active overvoltage detection and protection for overvoltage

The invention comprises an n-bit analog-to-digital flash converter comprising 2.sup.n /2 input comparators, each having a first input coupled to receive the analog voltage to be converted and a second input coupled to a different reference voltage. The reference voltages of each consecutive input comparator are spaced apart two LSBs of the converter. Each input comparator has two output, OUT and an inverted version thereof, OUT. 2.sup.n -1 consecutive latches are provided. Every other latch receives at its inputs the OUT and OUT signals from a single associated input comparator. All other latches receive the OUT signal of one of the input comparators and the OUT signal of an adjacent input comparator. The latches having inputs coupled to the OUT and OUT signals of a single input comparator produce a comparison output which change state every two LSBs of the converter and the latches having one input coupled to the OUT signal of one input comparator and the OUT signal of an adjacent input comparator produce comparison signals which change state halfway between the output signals of the adjacent latches. Thus, a comparison output is provided for every LSB of the full scale range of the converter using only 2.sup.n /2 input comparators.

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Greensboro, NC, United States of America

Charles D Lane