Digital waveform generator and method for synthesizing periodic analog waveforms using table readout of simulated .DELTA.- .SIGMA. analog-to-digital conversion data

A digital waveform generator for generating periodic analog waveforms, comprising:

• a memory that stores a sequence of L samples of 1-bit delta-sigma (.DELTA..SIGMA.) analog-to-digital conversion data generated at a simulation frequency where L is equal to an integer multiple of said simulation frequency divided by a specified waveform frequency such that said L samples represent an integral number of periods of a periodic analog waveform at said specified waveform frequency, and which includes quantization noise that is shifted in frequency away from said waveform frequency, said memory having an input for receiving a first clock signal that cyclically reads out the data from said sequence at a constant information rate;
• a 1-bit digital-to-analog converter (CAD) that converts said data into an analog waveform in response to a second clock signal;
• an output filter that averages the analog waveform and removes the shifted quantization noise to produce a synthesized waveform at said waveform frequency that approximates the periodic analog waveform;
• a first relatively low speed high integration chip that includes said memory, said memory being configured to read out N-bit words at a time in response to the first clock signal;
• and
• a second relatively high speed low integration chip that includes a parallel-to-serial converter that converts successive N-bit words into N 1-bit words in response to the second clock signal, said CAD and said output filter, said second clock signal having a frequency that is N times the frequency of said first clock signal so that the information rate read out of the memory equals that set by the CAD and the data read out of said memory is identical to the data presented to the CAD.

A digital waveform generator for generating periodic analog waveforms, comprising:

• a first relatively low speed high integration chip that includes a memory that stores a sequence of p-bit delta-sigma (.DELTA..SIGMA.) analog-to-digital conversion data, said sequence representing an integral number of periods of a periodic analog waveform having a known waveform frequency, and includes quantization noise that is shifted in frequency away from said waveform frequency, said memory having an input for receiving a first clock signal that cyclically reads out N-bit words from said sequence at a constant information rate;
• a second relatively high speed low integration chip that includes a downconverter that converts successive N-bit words into multiple p-bit words in response to a second clock signal, a p-bit digital-to-analog converter (DAC) that converts each successive p-bit word into an analog waveform in response to a second clock signal, and an output filter that averages the analog waveform and removes the shifted quantization noise to produce a synthesized waveform at said waveform frequency that approximates the periodic analog waveform, said second clock signal having a frequency that is N times the frequency of said first clock signal so that the information read out of the memory equals that set by the DAC, said second chip's relatively low levels of circuit integration limiting the number of bits that the downconverter can convert at each cycle of the second clock signal to N/A bits;
• and
• a third intermediate speed intermediate integration chip that includes a speedup buffer, said speedup buffer responding to a third clock signal whose frequency lies between that of the first and second clock signals to convert successive N-bit words into N/A bit words at the constant information rate such that said downconverter converts successive N/A bits into p-bit words in response to the second clock signal.

A digital waveform generator for generating periodic analog waveforms, comprising:

• a memory that stores a sequence of L samples of 1-bit delta-sigma (.DELTA..SIGMA.) analog-to-digital conversion data generated at a simulation frequency where L is equal to an integer multiple of said simulation frequency divided by a specified waveform frequency such that said L samples represent an integral number of periods of a periodic analog waveform at said specified waveform frequency, and which includes quantization noise that is shifted in frequency away from said waveform frequency, said memory having an input for receiving a first clock signal that cyclically reads out the data from said sequence at a constant information rate;
• a 1-bit digital-to-analog converter (DAC) that converts each successive 1-bit word into an analog waveform in response to a second clock signal;
• and
• an output filter that averages the analog waveform and removes the shifted quantization noise to produce a synthesized waveform at said waveform frequency that approximates the periodic analog waveform;
• wherein said quantization noise in said sequence has a null near said waveform frequency and a band stop shape that rolls off with a known order, said output filter comprising a band pass filter that tracks the waveform frequency to produce the synthesized waveform and whose order is at least one greater than that of the quantization noise.

A digital waveform generator for generating periodic analog waveforms, comprising:

• a memory that stores a sequence of L samples of 1-bit delta-sigma (.DELTA..SIGMA.) analog-to-digital conversion data generated at a simulation frequency where L is equal to an integer multiple of said simulation frequency divided by a specified waveform frequency such that said L samples represent an integral number of periods of a periodic analog waveform at said specified waveform frequency, and which includes quantization noise that is shifted in frequency away from said waveform frequency, said memory having an input for receiving a first clock signal that cyclically reads out the data from said sequence at a constant information rate;
• a 1-bit digital-to-analog converter (DAC) that converts each successive 1-bit word into an analog waveform in response to a second clock signal;
• and
• an output filter that averages the analog waveform and removes the shifted quantization noise to produce a synthesized waveform at said waveform frequency that approximates the periodic analog waveform;
• wherein said 1-bit DAC converts each 1-bit word into a selected one of a plurality of waveform levels, further comprising an amplitude adjustment circuit that scales the waveform levels to adjust the amplitude of the synthesized waveform, said synthesized waveform having a constant signal-to-noise ratio (SNR) regardless of amplitude.

A digital waveform generator for generating periodic analog waveforms, comprising:

• a memory chip having a relatively low speed and high level of circuit integration that stores a sequence of 1-bit delta-sigma (.DELTA..SIGMA.) analog-to-digital conversion data, said sequence representing an integral number of periods of a periodic analog waveform having a known waveform frequency, and includes quantization noise that is shifted in frequency away from said waveform frequency, said memory being configured to cyclically read out N-bit words from said sequence at a constant information rate in response to a low frequency clock signal;
• a speed up chip having a relatively intermediate speed and intermediate level of circuit integration that converts successive N-bit words into N/A-bit words in response to an intermediate frequency clock signal that maintains the constant information rate;
• and
• a conversion chip having a relatively high speed and low level of circuit integration that comprises:
• a parallel-to-serial converter that converts the next N/A bits into a serial bit stream in response to a high frequency clock signal;
• a 1-bit digital-to-analog converter (DAC) that converts the serial bit stream into an analog waveform having binary levels at said high frequency clock signal;
• an amplitude adjustment circuit for scaling the binary levels;
• and
• an output filter that averages the scaled analog waveform and rejects the shifted quantization noise to produce a synthesized waveform at said waveform frequency that approximates the periodic analog waveform with a constant signal-to-noise ratio that is independent of the synthesized waveform's amplitude.

A digital waveform generator for generating periodic analog waveforms, comprising:

• a computer that is programmed to simulate a p-bit delta-sigma (.DELTA..SIGMA.) analog-to-digital conversion (ADC) modulator and receives as inputs a selection of a periodic analog waveform, a waveform frequency, a simulator clock frequency, a filter type and its order and outputs a bitstream that includes quantization noise that is shaped away in frequency from said waveform frequency;
• a memory chip having a relatively low speed and level of circuit integration that stores L samples of said bitstream at a resolution of p-bits per sample, said waveform frequency being equal to an integer multiple of said simulator clock frequency divided by the number of samples L such that the L samples represent an integral number of periods of the periodic analog waveform, said memory being configured to cyclically read out N-bit words in parallel from said sequence at a constant information rate equal to the product of the simulator clock frequency and the p-bits per sample in response to a low frequency clock signal;
• and
• a conversion chip having a relatively high speed and low level of circuit integration comprising:
• a downconverter that converts successive N bit words at the low frequency clock signal into a p-bit bit stream at a high frequency clock signal that maintains the constant information rate;
• a p-bit digital-to-analog converter (DAC) that converts the p-bit bit stream into a multi-level analog waveform at said high frequency clock signal;
• and
• an output filter that averages the analog waveform and removes the shifted quantization noise to produce a synthesized waveform at said waveform frequency that approximates the periodic analog waveform.

A method of generating periodic analog waveforms, comprising:

• selecting a periodic analog waveform, a waveform frequency, a simulation frequency, a bit rate p, and a filter order;
• simulating a p-bit delta-sigma (.DELTA..SIGMA.) analog-to-digital conversion (ADC) modulator for the selected periodic analog waveform and frequency with said filter order at said simulation frequency to output a bitstream that includes quantization noise that is shaped in frequency away from said waveform frequency;
• storing L samples of said bitstream at p-bits per sample where L is equal to an integer multiple of said simulation frequency divided by the waveform frequency such that said L samples represent an integral number of periods of the periodic analog waveform at said waveform frequency;
• cyclically reading out the samples at a constant information rate;
• converting the p-bit words into a multi-level analog waveform at the simulation frequency to maintain the constant information rate;
• and
• filtering the analog waveform with an output filter whose order is at least one greater than the filter order used in the simulation to average the analog waveform and remove the shaped quantization noise to produce a synthesized waveform at said waveform frequency that approximates the periodic analog waveform.

A method of generating periodic analog waveforms, comprising:

• selecting a periodic analog waveform, its frequency, a simulation frequency, a bit rate p, and a filter order;
• simulating a p-bit delta-sigma (.DELTA..SIGMA.) analog-to-digital conversion (ADC) modulator for the selected periodic analog waveform and frequency with said filter order at said simulation frequency to output a bitstream that includes quantization noise that is shaped in frequency away from said waveform frequency;
• storing L samples of said bitstream at p-bits per sample in memory having a relatively low speed and high level of circuit integration, said L samples representing an integral number of periods of the periodic analog waveform;
• cyclicallv reading out the samples in parallel as N-bit words in response to a low frequency clock signal at a constant information rate;
• converting successive N-bit words into p-bit words in response to a high frequency clock signal using a converter having a relative high speed and low level of circuit integration;
• converting the p-bit words into a multi-level analog waveform in response to the high frequency clock signal using a digital-to-analog converter (DAC) having the same high speed and low level of circuit integration as said converter such that the information rate remains constant;
• and
• filtering the analog waveform with an output filter whose order is at least one greater than the filter order used in the simulation to average the analog waveform and remove the shaped quantization noise to produce a synthesized waveform at said waveform frequency that approximates the periodic analog waveform.

A digital waveform generator for generating periodic analog waveforms, comprising:

• a memory that stores a plurality of sequences representing the same periodic analog waveform at different discrete waveform frequencies, said sequences including L samples of 1-bit delta-sigma (.DELTA..SIGMA.) analog-to-digital conversion data generated at a simulation frequency where L is equal to respective integer multiples of said simulation frequency divided by the respective waveform frequencies such that said L samples represent different integral numbers of periods of the periodic analog waveform at the discrete waveform frequency, said analog waveforms having quantization noise that is shifted in frequency away from said waveform frequency, said memory having an input for receiving a first clock signal that cyclically reads out the data from one said sequence at a constant information rate;
• an interface circuit for selecting one of said sequences;
• a 1-bit digital-to-analog converter (DAC) that is clocked at the simulation frequency to converts each successive 1-bit word into an analog waveform that maintains the constant information rate;
• and
• an output filter that averages the analog waveform and removes the shifted quantization noise to produce a synthesized waveform at the selected discrete waveform frequency that approximates the periodic analog waveform.