Abstract: A direct digital synthesizer (30) with noise shaping circuitry can comprise a ROM-less direct digital synthesizer having a quantizer (40) and a noise shaping loop incorporating the quantizer for shaping a quantization noise due to noise from the quantizer. The noise shaping loop can comprise a noise shaping filter (44) and the noise shaping loop can feed back to the noise shaping filter a difference between an input signal (49) to the quantizer and an output signal (43) from the quantizer. The ROM-less direct digital synthesizer can further include a dither (39) combined at an input of the quantizer.

Abstract: A non-integer fractional divider divides a reference clock signal having period P by a non-integer ratio K. The divider includes multiplexers to receive a plurality N of clock signals wherein each clock signal is equally phase shifted by a P/N delay. Incrementers coupled to the multiplexers select first and second clock signals between the N clock signals. Such that the phase shift delay between the two selected clock signals is representative of the non-integer value of K. The selected clock signals are combined to output a divided clock signal. The enabling time of each selected clock signal is respectively representative of the duration of the low level and the high level of the divided clock signal.

Abstract: A direct digital synthesizer that suppresses phase jumps which would invite the generation of spurious signals. Out of phase data supplied by a phase accumulator, the value of any rounding error arising at the time of phase computation is entered into a variable delay circuit, and the phase of a signal obtained by phase-amplitude conversion is controlled to compensate for any phase jump in the output signal.

Abstract: A DDS (Direct Digital Synthesis) frequency synthesizer can be adapted to operate as a pseudo random noise generator by including a swept address ingredient that distributes (but does not eliminate) repetitive frequency components that would otherwise appear in the output of the basic DDS technique, (which fetches fixed but randomized values from a waveform memory). These residual distributed long period frequency components in the output of a swept DDS pseudo random noise generator are suppressed by making the sweep itself irregular. The noise generator includes an Address Increment Register (AIR) whose content: (1) alters the address used to fetch fixed randomized values from the waveform memory; and (2) is incremented to produce the swept address (different sequences of addresses). At some point the AIR value has been incremented as high as it will go (i.e., the end of the sweep has been reached), and the process must start over.

Abstract: A waveform generator for use in IQ modulation in a wireless cellular device having an FM waveform generator (104) that is programmable to generate a desired FM frequency deviation; a digital accumulator (108, 110, 112) to provide phase generation.

Abstract: An amplitude data generator receives L-bit data, and outputs amplitude data of a predetermined periodic function of a phase specified by the data. A frequency setter sets frequency data of (K+L−1) bits obtained by dividing a desired output frequency by a frequency of a predetermined clock signal. A K bit counter counts the clock signal. L-set product and sum computation circuits subject the frequency data of (K+L−1) bits into L-set K-bit data in which a start bit is shifted by one bit each other. Then, these circuits compute a logical product between the counter output of K bits from the counter and a bit unit, and obtains a total number of bits for each set when the computation result is 1. A shifting/adding circuit adds each total number data obtained by the L-set product and sum computation circuits by shifting a bit, and outputs the least significant L bits of the computation result to the amplitude data generator.

Abstract: A phase-to-sinusoid-amplitude conversion system and method for use in, for example, direct digital frequency synthesizer applications. The system and method convert phase data to signal amplitude data using an approximation of the first quadrant of a sine function using a plurality of linear line segments of preferably equal length. Each segment is defined with a lower horizontal-axis bound; a lower vertical-axis bound; and a slope represented as a sum of a plurality of slope elements. Based on the approximation and for a given phase angle a set of values are evaluated, for each linear line segment, representing a product of (i) a horizontal displacement representing a difference between the prescribed phase angle and the lower horizontal-axis bound xi of a selected linear line segment where, for example, xi<X<xi+1 and (ii) each one of the slope elements of the selected linear line segment.

Abstract: A clock signal generator having a DDS circuit which adds up a frequency word with a particular frequency and generates an output pulse when an overflow occurs. To reduce jitter, a parameter value corresponding to the ideal overflow time of the DDS circuit is determined and an output pulse generating circuit determines, in dependence on the parameter value and using a further, higher frequency, a corrected time for the output pulse and outputs the output pulse at this corrected time.

Abstract: A system and method for configuring an automatic test system to produce a plurality of clocks from a reference clock includes a user interface and software. The user interface receives a plurality of inputs that specify desired frequencies of the plurality of clocks. In response to a command from the user interface, the software calculates values for dividers coupled to the reference clock, for deriving each of the desired frequencies from the reference clock. According to one embodiment, the desired frequencies form ratios that must be met to satisfy coherence. In calculating the divider values, the software minimizes frequency errors while precisely preserving the required ratios.

Abstract: An apparatus and method are provided for synthesizing a variable frequency sinusoidal waveform. The apparatus and method exploit octant symmetry properties of sine and cosine waveforms, when taken together. The digital frequency synthesis apparatus includes a phase signal and a phase-to-amplitude converter. The phase signal indicates a desired phase angle of the sinusoidal waveform. The phase-to-amplitude converter is coupled to the phase signal. The phase-to-amplitude converter provides a desired amplitude sample corresponding to the desired phase angle, where the desired amplitude sample is derived from amplitude samples corresponding to an octant of the sinusoidal waveform. The phase-to-amplitude converter includes a Haar Transform-based coarse octant amplitude sample generator that computes Haar coefficients corresponding to the phase signal and transforms the Haar coefficients into the desired amplitude sample.

Abstract: Accumulator 201 accumulates data K (K: integer) for every clock and outputs a carry-out signal at the time of an overflow. Random signal generator 202 outputs a random signal for every clock. Adder 203 adds the carry-out signal and random signal to data M (M: integer), changes the frequency dividing ratio randomly and converts spurious to white noise. This makes it possible to optimally maintain the spurious characteristic, shorten the lockup time and reduce power consumption.

Abstract: A digital synthesizer includes a memory containing values representing amplitudes of a signal such as a sinewave, a digital/analog converter for converting outputs from the memory into an analog signal, and a counter for counting by a predetermined fixed increment, which operates at a high frequency to enable the generation of very precise frequency waveforms. The digital synthesizer has many practical applications including the generation of precise signals to extract information from input radio frequency signals, the obtaining of a precise frequency from a low-cost clock, and the use as a component of a FSK modulator to permit selection between signals of multiple frequencies without any phase discontinuity. Finally, the digital synthesizer can be used in combination with an 8-bit memory, to generate a 10-bit input to a digital-to-analog converter.

Abstract: A digital frequency synthesizer includes a clock which produces a clock signal oscillating at a fixed frequency and a delay line which receives the clock signal and which produces therefrom a plurality of phase shifted clock signals oscillating at the fixed frequency. Each phase shifted clock signal is shifted in phase with respect to the clock signal and with respect to the other phase shifted clock signals. A look-up table receives an address value related to an ideal phase shifted clock signal oscillating at the fixed frequency and outputs a tap address related to the address value. A selection circuit receives the plurality of phase shifted clock signals and the tap address and outputs one of the phase shifted clock signals in response thereto. A sampling circuit samples at least a portion of the one phase shifted clock signal output by the selection circuit and outputs the sampled portion to form at least a part of an oscillator signal having a desired frequency.

Abstract: A frequency dither technique is used for reducing spurs due to phase increment errors in a direct digital synthesizer output sinusoid. The spurs for a desired output frequency are calculated and, if the spurs fall within a phase locked loop bandwidth, a pair of phase increment values are used representing a pair of frequencies that average to the desired output frequency and the spurs of which fall outside the phase locked loop bandwidth.

Abstract: A direct digital synthesizer (200) includes a first accumulator (202) that acts as the frequency accumulator in order to generate the desired average frequency. A second accumulator (204) acts to generate a phase correction at each overflow, with the input into the phase correction accumulator (204) being a function of the input frequency. The clock signal of the phase correction accumulator (204) is the overflow signal (208) of the frequency accumulator (202). With this configuration, the frequency accumulator (202) generates the timing, and the phase correction accumulator (204) generates the interpolation value. The use of the two accumulators (202, 204) as described, eliminates the need to use a multiplier in the design which is a high current consumption device.

Abstract: A direct-digital synthesizer for generating a waveform includes a digital accumulator fed by a phase increment word and a series of clock pulses for successively adding the phase increment word to produce a series of N bit phase words. A table or trigonometric engine produces sine and cosine digital signals related to the M most significant bits of the phase word produced by the accumulator. A feedback loop is fed by truncation error words comprising at least a portion of N-M least significant bits of the N bit phase words producing truncation error compensation words. The feedback loop includes a digital filter. The feedback loop includes a digital filter. The feedback loop including the digital filter provides a low pass truncation error response to the truncation error having at least one zero in the transfer function thereof at DC.

Abstract: A direct digital frequency synthesizer and a hybrid frequency synthesizer combining the direct digital frequency synthesizer and a phase locked loop is provided. The direct digital frequency synthesizer includes a phase accumulator that is configured to generate a discrete phase signal. Spurious phase modulation in the discrete phase signal is reduced by a noise shaper, and the output of the noise shaper is then used to address a phase-to-amplitude translator. The phase-to-amplitude translator generates a discrete waveform which is converted to a continuous waveform by a digital to analog converter. The hybrid frequency synthesizer uses a mixer to combine a reference frequency generated by a reference source and a DDFS output signal generated by a direct digital frequency synthesizer. The output from the mixer is then coupled to the input of a phase locked loop which multiplies the mixer output to generate the frequency synthesizer output.

Abstract: A method for synthesizing a clock signal, said clock signal being locked to a reference clock signal, said method providing for using a third clock signal, operating at a higher frequency. The method provides the steps of: measuring the reference clock signal (CK_REF) by means of the third clock signal (CK_HIGH), operating at a higher frequency, obtaining a measured value (MES) of the reference clock signal (CK_REF) frequency; comparing the measured value (MES) with a nominal value; obtaining a correction value (CRR) as a function of the measured value (MES) and storing said correction value (CRR); using said correction value (CRR) for driving a digital controlled oscillator (OC) that outputs the synthesized clock signal (CK_SYN).

Abstract: An electronic system, such as a video decoder (80), includes a clock generator circuit (22, 22′) based upon a phase-locked loop (PLL) (25). The PLL (25) includes a voltage controlled oscillator (VCO) (30) that produces a plurality of evenly-spaced output phases, each of a locked frequency relative to a reference clock (CREF). A frequency synthesis circuit (27) receives a frequency selection value on control lines (FREQ) that include an integer and a fraction portion. The integer and fraction portion of the frequency selection value are added to the current contents of a register (40) that stores the previous integer value used to select the corresponding phase from VCO (30) for application to the clock input of a toggle flip-flop (36) from which the output clock (COUT) is generated. Use of the fraction portion permits a time-averaged clock frequency to be produced with more precision than the multiple phases output by the VCO (30).

Abstract: An amplitude data generator receives L-bit data, and outputs amplitude data of a predetermined periodic function of a phase specified by the data. A frequency setter sets frequency data of (K+L−1) bits obtained by dividing a desired output frequency by a frequency of a predetermined clock signal. A K bit counter counts the clock signal. L-set product and sum computation circuits subject the frequency data of (K+L−1) bits into L-set K-bit data in which a start bit is shifted by one bit each other. Then, these circuits compute a logical product between the counter output of K bits from the counter and a bit unit, and obtains a total number of bits for each set when the computation result is 1. A shifting/adding circuit adds each total number data obtained by the L-set product and sum computation circuits by shifting a bit, and outputs the least significant L bits of the computation result to the amplitude data generator.

Abstract: A digital frequency synthesizer comprises means for the generation of the samples of a digital signal to be converted into an analog signal encoded on N bits as a function of a frequency control word, means for the generation of a noise signal encoded on N bits, and a digital-analog converter, the useful signal and the noise signal being truncated to M bits before being added up by an adder. The result of the addition is converted into analog signal form by the digital-analog converter. The generated noise has at least a noise density substantially equal to a law of equiprobability, this density being zero outside a given space. Application especially to direct digital synthesis, for example in the field of radar techniques or that of instrumentation.

Abstract: An inexpensive numerically-controlled fast frequency-hopping microwave synthesizer. A voltage-controlled oscillator (VCO) output phase remains locked to an internal direct digital synthesizer (DDS) reference signal over the entire output frequency band, which is an order of magnitude larger than the internal sampling clock frequency. A “Nyquist-boundary hopping” scheme compares signals from an alias band of the DDS with signals from an alias band of the sampled VCO output to derive an output phase error signal, which is forced to zero in a manner that locks the VCO output phase to the DDS output phase over a frequency hop-distance greater than the DDS bandwidth. Accordingly, in a single second, the synthesizer can hop phase-continuously in a single clock cycle to each of hundreds of thousands of different microwave output frequencies with relatively low clock rates (up to 100 MHz) commensurate with silicon application-specific integrated circuits (ASICs).

Abstract: A system and method for reducing the computational complexity of the calculations performed by a Numerically Controlled Oscillator (NCO). Through exploitation of mathematical symmetries and other techniques, the size of a lookup table of sinusoidal values employed by the NCO to approximate sinusoids may be reduced by the combination of different frequency shifts.

Abstract: An improved circuit and technique for obtaining phase-coherent synthesis using a direct digital synthesizer (DDS). In the phase-coherent frequency synthesis device of the invention, a computational engine constructed from a large programmable gate array, a digital signal processing microprocessor, or a number of discrete digital logic blocks generates information sent to the DDS for generating an output frequency, .function..sub.out, which is in phase with all previous outputs of the device at the same frequency.

Abstract: A direct digital frequency synthesizer includes inputs for a reference clock signal and a control word, and an output for a synthesized clock signal. A phase accumulator coupled to the input for the control word and the reference clock signal has an output for a phase control signal. A phase shifter has inputs for the reference clock signal and the phase control signal and an output coupled to the output for the synthesized clock signal. The control word can be used to adjust the output frequency and phase of the synthesized clock signal.

Abstract: A frequency synthesizer comprises a direct digital frequency synthesizer (DDFS), which provides in-phase and quadrature sinewave signals at a preset frequency from digital analogue converters respectively, and a balanced mixer. The balanced mixer provides an output signal having a carrier frequency twice that provided by DDFS and reduced levels of spurious signals. A signal having a desired frequency is generated by controlling the DDFS to generate sinewave output signals at half the desired frequency. The reduced levels of spurious signals obtained by the arrangement allows improved signals for use in, for example, local oscillator applications.

Abstract: A direct digital synthesizer circuit and method for reducing the harmonic content in a synthesized output signal. The direct digital synthesizer generates first and second address signals driving first and second sine look-up read only memory (sine ROM) circuits. The first and second sine ROMs generate first and second digital sine wave signals which are offset in phase from one another by 180 degrees. The first and second digital sine wave signals are converted to first and second analog sine wave signals. The first and second analog sine wave signals are combined in a subtractor circuit. As a result of the phase relationship between the first and second analog sine wave signals, the fundamental component of these signals are emphasized by subtraction while the second harmonic component of theses signals are simultaneously de-emphasized.

Abstract: A direct digital frequency synthesizer for generating a digital sine or cosine function waveform receive digital input. Memory stores digital samples along portions of sine and cosine function waveforms. The memory outputs the digital samples in response to a first portion of the digital input. Control logic is responsive to the digital input and controls the output of the digital samples from the memory to allow digital samples along a complete cycle of the sine or cosine function waveform to be output even though only portions of the sine and cosine function waveforms are stored in the memory. A linear interpolator receives a second portion of the digital input and modifies digital samples output by the memory to generate intermediate digital samples between the digital samples stored in the memory to improve accuracy.

Abstract: A digital frequency synthesizer for generating square wave signals employing a phase accumulator, triangle wave logic function, smoothing filter, and hard limiter. A triangle wave logic function simplifies the implementation of stable square wave signals.