Analog Devices,inc.

David T Crook

Thomas E Tice

Charles D Lane

Kevin M Kattmann

John Jerome Kornblum

Reuben Pascal Nelson

Ken Gentile

Ernest T Stroud

Roger B Huntley, Jr

Jon T Baird

James A Surber, Jr

Synthesizers are provided to generate synthesizer signals in response to primary digital signal representations that are created by a signal generator. In an important feature, the synthesizers further include a signal corrector that inserts correction digital signal representations to at least partially cancel a corresponding spurious component in the primary digital signal representation and thereby provide synthesizer signals with reduced spurious content.

Synthesizer structures and methods that reduce spurious signals

Feedback methods and systems are provided to achieve rapid switching of oscillator frequencies without compromising operational feedback loop bandwidths that filter out spurious tones and phase noise to thereby enhance loop spectral and noise performance. The methods respond to frequency changes in a reference signal by providing an open-loop drive current to drive a feedback signal towards the reference signal. The drive current is terminated and the feedback control loop closed when the feedback signal is within a predetermined acquisition range of the reference signal. Preferably, the closed loop is initially configured with a first feedback bandwidth and is subsequently reconfigured with a second steady-state feedback bandwidth that is less than the first feedback bandwidth. The invention also provides a feedback control system that practices the invention's methods

Feedback methods and systems for rapid switching of oscillator frequencies

Feedback control loop systems are provided that enhance output-signal switching times without degrading other loop performance parameters. The systems reduce &ldquo;kick-back&rdquo; voltages that are generated in a loop filter by drive currents which rapidly drive a control loop oscillator to a loop acquisition range. This reduction reduces a frequency step in the oscillator output signal which would otherwise have to be driven to eliminate the frequency step with a consequent increase in the output-signal switching time. Structures are provided that reduce the kick-back voltage to thereby enhance output-signal switching times.

Feedback systems for enhanced oscillator switching time

Feedback methods and systems are provided to achieve rapid switching of oscillator frequencies without compromising operational feedback loop bandwidths that filter out spurious tones and phase noise to thereby enhance loop spectral and noise performance. The methods respond to frequency changes in a reference signal by providing an open-loop drive current to drive a feedback signal towards the reference signal. The drive current is terminated and the feedback control loop closed when the feedback signal is within a predetermined acquisition range of the reference signal. This is determined by successively comparing a feedback frequency of the feedback signal to a destination frequency of the reference signal over a comparison window of time. The invention also provides a feedback control system that practices the invention's methods.

Adaptive feedback-loop controllers and methods for rapid switching of oscillator frequencies

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 drive circuit and method for shaping the pair of complementary digital signals that drive a conventional CMOS switch are presented. The method adjusts the digital signals' duty cycles to set their cross point voltage levels so that at the cross points the voltage level at the CMOS switch's reference node is undisturbed with respect to its fully switched level. The drive circuit includes two pair of diode connected PMOS load transistors and NMOS load transistors that are connected at a pair of output terminals and a pair of switches. In one state, the NMOS load transistor is turned on while the switch cuts off its signal current so that the shaped digital signal's voltage at the output terminal is reduced to a precision limited low voltage. In the other state, the NMOS load transistor is turned off while the switch directs the signal current through the PMOS load transistor so that the shaped digital signal's voltage at the output terminal is increased to the PMOS load transistor's gate-to-source voltage. The CMOS transistors' channel geometries and the amount of signal current are selected to set the duty cycle of the shaped digital signals and thereby set the optimum cross point voltage levels.

Drive circuit and method for controlling the cross point levels of a

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.

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Summerfield, NC, United States of America

David T Crook