Analog Devices,inc.

Thomas E Tice

David T Crook

Charles D Lane

Kevin M Kattmann

Roger B Huntley, Jr

James A Surber, Jr

A dual-tunable direct digital synthesizer is provided with a programmable frequency multiplier that multiplies a relatively low frequency fixed clock signal F.sub.clk so that the output frequency F.sub.o of the waveform is:

Dual tunable direct digital synthesizer with a frequency programmable

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

A flash converter in which an input circuit is provided for maintaining a substantially constant collector-base voltage on the input emitter-followers, so as to obviate the distortion caused by variation of the input capacitance with input voltage. The driving source directly drives the base of the emitter-followers and, through a level-shift circuit, also drives the collectors of the emitter-follower transistors.

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Greensboro, NC, United States of America

Thomas E Tice