Digital multifrequency signal generator

Claim 2

In a digital signal generator of the type including at least one controllable digital divider for selectively generating pulse signals at each of a plurality of frequencies of intereSt and at least one filter for converting the pulse signals to sine-wave signals, the improvement which comprises, means responsive to the pulse signals from the digital divider for generating a pulsating signal having a substantially rectangular waveform in which the pulse width of at least the initial pulse of said pulsating signal generated at each frequency of interest is less than the pulse width of subsequent pulses of said pulsating signal during each interval that said pulsating signal is generated, the pulse width of said initial pulse and the pulse width of said subsequent pulses being in a prescribed relationship for minimizing transient signal components in the resulting sine-wave output from the filter.

Claim 3

Apparatus as defined in claim 1 wherein said pulsating signal generating means includes digital counting means controllably settable to a prescribed initial condition upon initiating generation of a signal at each of the frequencies of interest and controllable means responsive to a control signal and a pulsating output signal from said counting means for generating said pulsating signal in which the pulse width of the initial pulse generated at each frequency is less than the pulse width of subsequent pulses generated at each frequency.

Claim 4

The apparatus as defined in claim 2 wherein the frequency of the pulse signals from the divider is four times the frequency of the desired sine-wave signal and said digital counting means includes a plurality of stages arranged to effect a divide-by-four function, and further including means responsive to said control signal for setting each stage of said mounting means to an initial count of one upon initiating generation of a signal at each of the frequencies of interest.

Claim 5

The apparatus as defined in claim 3 wherein said signal generating means further includes means for yielding a pulsating signal having a substantially zero average value.

Claim 6

The apparatus as defined in claim 1 further including means for adjusting the amplitude of said pulsating signal at each frequency of interest to a predetermined level, said predetermined level being determined in accordance with the attenuation versus frequency characteristic of the filter so that the amplitude of the sine-wave output from the filter is constant for all frequencies of interest.

Claim 7

Apparatus as defined in claim 3 wherein said controllable means is a tri-state logic gate.

Claim 8

In a digital signal generator of the type including at least one controllable digital signal source for selectively generating pulse signals at each of a plurality of frequencies of interest, apparatus for converting the pulse signals to pulsating signals having a substantially rectangular waveform and a low-pass filter for converting the pulsating signals to sine-wave signals, characterized in that, the low-pass filter has an attenuation versus frequency characteristic having a corner frequency at a frequency less than the highest frequency of interest and including means for adjusting the amplitude of the individual pulsating signals at each frequency of interest to a predetermined level, said predetermined level being determined in accordance with the attenuation versus frequency characteristic of the low-pass filter so that the amplitude of the sine-wave output from the filter is constant for all frequencies of interest.

Claim 9

In a digital signal generator of the type including at least one controllable digital signal source for selectively generating pulse signals at each of a plurality of frequencies of interest, apparatus for converting the pulse signals to pulsating signals having a substantially rectangular waveform and a low-pass filter for converting the pulsating signals to sine-wave signals, characterized in that, the low-pass filter has an attenuation versus frequency characteristic having a corner frequency at a frequency less than the highest frequency of interest and including means for adjusting the amplitude of the individual pulsating signals at each frequency of interest to a predetermined level, said predetermined level being determined in accordance with the attenuation versus frequency characteristic of the low-pass filter so that the amplitude of the sine-wave output from the filter is constant for all frequencies of interest.

Claim 10

Apparatus as defined in claim 7 wherein said amplitude adjusting means includes controllable means responsive to individual control signals assigned to the individual frequencies of interest for adjusting the amplitude of said pulsating signal to said predetermined levels assigned to each of said frequencies of interest.

Claim 11

Apparatus as defined in claim 8 wherein said amplitude adjusting means further includes a plurality of impedance means in circuit relationship with said controllable means and a summing point, each of said impedance means being assigned to a frequency of interest and having a prescribed component value determined in aCcordance with the attenuation versus frequency characteristic of the low-pass filter for adjusting the amplitude of said pulsating signal at the assigned frequency of interest so that the sine-wave output from said filter has a predetermined amplitude.

Claim 12

Apparatus as defined in claim 9 wherein said controllable means includes a plurality of controllable gate means in circuit relationship with the pulsating signal generating apparatus and in one-to-one circuit relationship with said impedance means, each of said controllable gate means being responsive to a supplied control signal for supplying a version of said pulsating signal to an associated one of said impedance means.

Claim 13

Apparatus as defined in claim 10 wherein each of said controllable gate means is a logic gate having a plurality of inputs and an output, said logic gates being responsive to predetermined signals supplied to said inputs to yield a high state output for a first predetermined combination of input signals, a low state output for a second predetermined combination of input signals and an open circuit state output for a third predetermined combination of input signals, said pulsating signal being supplied to one of said inputs and said control signals being selectively supplied to another of said inputs.

Claim 14

Apparatus as defined in claim 7 wherein the apparatus for converting the pulse signals from the digital signal source to pulsating signals includes means responsive to the pulse signals for generating a pulsating signal having a substantially rectangular waveform in which the pulse width of at least the initial pulse of said pulsating signal at each frequency of interest is less than the pulse width of subsequent pulses of said pulsating signal, the pulse width of said initial pulse and the pulse width of said subsequent pulses being in a prescribed relationship for minimizing transient signal components in the resulting output from the filter.

Claim 15

Digital apparatus for generating multifrequency signals including combinations of a plurality of frequencies of interest which comprises: a low-pass filter having a predetermined attenuation versus frequency characteristic in which the corner frequency of said filter characteristic is at a frequency less than the highest frequency of interest; at least first and second controllable means supplied with clock pulses at a pre-established rate and being responsive to individual control signals for selectively generating pulsating signals at ones of said frequencies of interest corresponding to the supplied control signals, each of said controllable means including means for adjusting the amplitude of said pulsating signals at each frequency of interest to be a predetermined level, the predetermined level associated with each frequency of interest being determined in accordance with the attenuation versus frequency characteristic of said low-pass filter so that the amplitude of the output from said filter is a constant level for all frequencies of interest; and means for combining the pulsating signals from said at least first and second controllable means, the resultant combined signal being supplied to said low-pass filter.

Claim 16

Digital apparatus for generating multifrequency signals including combinations of a plurality of frequencies of interest which comprises: a low-pass filter having a predetermined attenuation versus frequency characteristic in which the corner frequency of said filter characteristic is at a frequency less than the highest frequency of interest; at least first and second controllable means supplied with clock pulses at a pre-established rate and being responsive to individual control signals for selectively generating pulsating signals at ones of said frequencies of interest corresponding to the supplied control signals, each of said controllable means including means for adjusting the amplitude of said pulsating signals at each frequency of interest to be a predetermined level, the predetermined level associated with each frequency of interest being determined in accordance with the attenuation versus frequency characteristic of said low-pass filter so that the amplitude of the output from said filter is a constant level for all frequencies of interest; and means for combining the pulsating signals from said at least first and second controllable means, the resultant combined signal being supplied to said low-pass filter.

Claim 17

Apparatus as defined in claim 13 wherein each of said controllable means further includes a programmable digital counter supplied with said clock pulses and responsive to said control signals for generating pulse signals at individual ones of the frequencies of interest and means for converting said pulse signals into pulsating signals having a substantially rectangular waveshape and a fundamental frequency at the frequency of interest being generated.

Claim 18

Apparatus as defined in claim 13 wherein the frequency of the pulse signal output from each of said digital counters of said first and second controllable means is at least four times the frequency of the signal being generated, and wherein said converting means includes digital means for dividing the pulse output from said counter by said at least fOur and means responsive to said control signals for setting said divider to a prescribed initial state at each frequency of interest and controllable gate means in circuit with said digital divider means and being responsive to said pulsating signal and said control signals selectively to generate a version of said pulsating signal in which the initial pulse of said version of said pulsating signal has a pulse width one-half the pulse width of subsequent pulses of said version of said pulsating signal at each frequency of interest.

Claim 19

The apparatus as defined in claim 15 further including means for biasing said combined signal so that the combined signal has a zero average value when supplied to said filter.