Bae Systems Information and Electronic Systems Integration Inc.

Bae Systems Information and Electronics Systems Integration Inc.

Steven E Turner

Joseph D Cali

Lawrence J Kushner

Michael P Anthony

Mark E Stuenkel

Curtis M Grens

Richard B Elder, Jr

Shailendra Srinivas

A direct digital synthesizer (DDS) circuit. The circuit includes a first input to receive a first fixed frequency clock signal having a first frequency, a second input to receive a second fixed frequency clock signal having a second frequency lower than the first frequency, and an output to provide an output frequency that is based at least in part on a frequency control word (FCW). The DDS circuit may include a frequency correction circuit having a first input to receive the first clock signal, a second input to receive the second clock signal, and a third input to receive the FCW, and an output to provide a frequency error of the first clock signal, the frequency error determined using the second clock signal and FCW. Alternatively, or in addition to, the DDS circuit may include an all-digital phase lock loop to correct for frequency wander of the first clock signal.

Direct digital synthesizer with frequency correction

Techniques are provided for phase coherent frequency synthesis. An embodiment includes a first phase accumulator to accumulate a frequency control word (FCW) at a clocked rate to produce a first digital phase signal representing phase data corresponding to phase points on a first sinusoidal waveform. The embodiment also includes a second phase accumulator to produce an incrementing reference count at the clocked rate and multiply it by the FCW to produce a second digital phase signal representing phase data corresponding to phase points on a second sinusoidal waveform. The multiplication is performed in response to change in the FCW. The embodiment further includes a multiplexer to select between the first and second digital phase signals based on completion of the multiplication. The embodiment also includes a phase-to-amplitude converter to generate digital amplitude data corresponding to the phase points on a sinusoidal waveform associated with the selected digital phase signal.

Phase coherent frequency synthesis

A clock distribution and alignment system includes at least three clock generators, each including a clock receiver circuit to receive a first clock signal having a first frequency, and a clock divider circuit to divide the received first clock signal into a second clock signal having a second frequency lower than the first frequency, each of two or more of the clock generators further including a phase detector circuit to compare the phase of the second clock signal with the phase of the second clock signal for a next one of the clock generators, and a clock adjuster circuit to adjust the phase of the received first clock signal based on the compared phases of the second clock signals. In some cases, the clock adjuster circuit is further to align the phases of the second clock signals to within a predefined tolerance of each other.

High-frequency clock distribution and alignment system

A true single-phase clocked multiplexer for outputting one of a plurality of input signals in synchronization with a clock signal and as selected by at least one select signal is provided. The multiplexer includes first transistors, second transistors, a first node between the first transistors, a second node between the second transistors, a third node coupled to the first node by one of the first transistors and to the second node by one of the second transistors, and a pre-charge transistor to couple the third node to a first voltage level. The first transistors are coupled to the first voltage level and configured to turn on in response to a gate voltage of a second voltage level different from the first voltage level. The second transistors are coupled to the second voltage level and configured to turn on in response to a gate voltage of the first voltage level.

Bandwidth extension for true single-phase clocked multiplexer

A digital to analog converter (DAC) circuit is disclosed which employs isolation providing cascode devices to reduce data dependent signal distortion. A DAC circuit configured according to an embodiment includes a current source associated with each bit of a digital word that is to be converted. Each current source is coupled to a current switch that is controlled by the associated bit. The DAC also includes a cascode device coupled to each of the current switches through a feed line. The DAC further includes a summing junction configured to generate an analog output signal corresponding to the digital word based on a sum of currents provided by the current sources, through the current switches and the feed lines. The cascode devices provide impedance matching and isolation between the feed lines and the summing junction to reduce signal reflections between the current switches and the summing junction to improve conversion performance.

Digital to analog converter with remote cascode devices

Frequency divider techniques are disclosed which can be used to address two problems: when an incorrect division occurs if the modulus control changes before the divide cycle is complete, and when an incorrect division occurs due to a boundary crossing (e.g., power-of-2 boundary crossing in a fractional-N PLL application). In one embodiment, a frequency divider is provided comprising a plurality of flip-flops operatively coupled to carry out division of an input frequency, and configured to generate a modulus output and receive a divided clock signal of a previous cell. An additional flip-flop is selectively clocked off one of the modulus output or the divided clock of the previous stage, depending at least in part on a Skip control signal applied to a data input of the additional flip-flop, and is further configured to selectively reset the plurality of flip-flops to a state that will result in a correct divide ratio.

Multi-modulus divider with power-of-2 boundary condition support

According to an embodiment, an improved flying adder circuit, comprises a fine clock, a coarse pulse clock, a rising edge triggered output connected to both the fine clock and the coarse pulse clock, a pulse clock connected to the rising edge triggered output, an adder, a 12-bit register situated to receive a signal from the adder and the pulse clock, and a single bit register situated to receive a signal from the pulse clock.

Modified flying adder architecture

A phase coherent fractional-N phase-locked loop synthesizer for maintaining phase coherence of a synthesized frequency includes a phase coherent delta-sigma modulator (DSM) having a plurality of feed-forward accumulator stages. The DSM is operatively coupled to a reference clock configured to generate a cyclical reference signal. The DSM configured to count a number of cycles of the reference signal, to cause, at each cycle of the reference signal, each of the stages of the DSM to accumulate a sum of a previous stage of the DSM, and to multiply each sum by a fractional divide word to produce a multiplier output, thereby causing the DSM to output a sequence of signals that tracks with the reference clock.

Modified delta-sigma modulator for phase coherent frequency synthesis applications

Techniques are provided for a switched output digital to analog converter employing an N-path cascode output switch. An example system may include a plurality of cascode transistors coupled in parallel to an output stage of a current mode digital to analog converter (DAC) circuit. The system may also include a plurality of control ports, each of the control ports coupled to a gate of one of the cascode transistors. The system may further include a plurality of output ports, each output port coupled to one of the cascode transistors. The cascode transistors are configured to switch the output stage of the DAC to the output port of the transistor in response to a routing control signal applied to the control port of the transistor. The cascode transistors are High Electron Mobility Transistors (HEMT) fabricated from Gallium Nitride.

N-path cascode transistor output switch for a digital to analog converter

In a fractional-n Phase Locked Loop the frequency control word multiplies by the output of a reference counter to provide the carry bit utilized in n/n+1 switching.

Coherent phase locked loop

A DDS system is disclosed that is configured to provide a variable clock delay that allows timing of data coming out of the ROM to be adjusted. In one example case, a DDS system is provided that includes a ROM for storing phase-to-amplitude conversion data and generating digital amplitude values corresponding to respective digital phase values, and delay circuitry for adjusting timing of data output by the ROM to compensate for propagation delay of the DDS system. The delay circuitry may include, for instance, delay elements that can be selected alone or in combination to adjust the timing. The timing can be adjusted, for example, by adjusting delay of a clock signal that clocks one or more ROM pipeline registers. The system may include a phase accumulator and DAC, and adjusting the timing may include adjusting delay of a clock signal that clocks one or more DAC pipeline registers.

ROM-based direct digital synthesizer with pipeline delay circuit

A phase accumulator generates phase data for a direct digital synthesis (DDS) device based on a reference phase to provide analog sinusoidal outputs that are locked to the reference phase and thus phase coherent. The frequency of a sinusoidal DDS output may be controlled by changing a frequency control word (FCW) provided to the phase accumulator without affecting the incrementing reference phase. The sinusoidal DDS output is based on a multiple of the FCW and the reference phase and thus remains locked to the reference phase, providing phase coherency even when the FCW changes to change the frequency.

Phase accumulator generating reference phase for phase coherent direct digital synthesis outputs

A digital to analog converter (DAC) method and apparatus employs a multiplying-adding DAC, eliminating digital adder circuitry. Examples are given for multiplying a 3-bit binary number by a 2-bit binary number; however, there are no limitations to the bit-widths of the numbers to be multiplied. The multiplying-adding DAC method can be scaled up or down in bit-width by feeding the DAC with partial sums and adjusting the DAC weights accordingly. An analog to digital converter (ADC) can be placed after the DAC to generate a digital output. By multiplexing preset digital data into the DAC core for return to zero (RTZ), a true zero that is the midpoint of the DAC output range is achieved. It does not return to a rail for single-ended outputs. RTZ in DAC circuits doubles the null frequency of sin(x)/x roll-off inherent in DACs and also helps reduce switching glitches in the DAC output.

Multiplying-adding return to zero digital to analog converter circuit and method

Techniques are disclosed for improving the dynamic performance of digital-to-analog converters (DAC), by compensating for the unique delay characteristics of each bit in the DAC summing junction to equalize the delays. In one example case, a DAC device is provided that includes a plurality of current sources and a plurality of switches, each switch operatively coupled between a corresponding one of the current sources and a summing junction that is operatively coupled to an analog output. The device further includes a plurality of switch control lines configured to receive a digital input, each switch control line for controlling a corresponding one of the switches. The device further includes a plurality of compensation delay elements, each associated with a corresponding one of the switch control lines and providing a different delay value.

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Nashua, NH, United States of America

Steven E Turner