Claims Analysis
Total Claims: 14
Claim 1
Independent Claim
157 words
In a modem, a modulator for modulating data, producing an output signal that conveys the data over a data channel at a data rate, said modulator comprising: (a) tone generation means for generating frequency shift keyed (FSK) tones that are modulated by the data about a first center frequency that is substantially different than a center frequency of the data channel that carries the output signal of the modulator; (b) a filter, coupled to the tone generation means to receive the modulated FSK tones, said filter producing a filtered signal having a bandwidth that is less than or substantially equal to the bandwidth of the data channel; and (c) means for frequency shifting the filtered signal so that a frequency spectrum of the modulated FSK tones comprising the filtered signal is contained within the data channel, thereby substantially eliminating an interference between positive and negative images of the frequency spectrum of the output signal of the modulator.
Claim 2
Dependent Claim
157 words
In a modem, a modulator for modulating data, producing an output signal that conveys the data over a data channel at a data rate, said modulator comprising: (a) tone generation means for generating frequency shift keyed (FSK) tones that are modulated by the data about a first center frequency that is substantially different than a center frequency of the data channel that carries the output signal of the modulator; (b) a filter, coupled to the tone generation means to receive the modulated FSK tones, said filter producing a filtered signal having a bandwidth that is less than or substantially equal to the bandwidth of the data channel; and (c) means for frequency shifting the filtered signal so that a frequency spectrum of the modulated FSK tones comprising the filtered signal is contained within the data channel, thereby substantially eliminating an interference between positive and negative images of the frequency spectrum of the output signal of the modulator.
Claim 3
Dependent Claim
42 words
The modulator of claim 1, wherein the first center frequency is substantially greater than the center frequency of the data channel, and wherein the means for frequency shifting the filtered signal shift it downwardly into the frequency spectrum of the output signal.
Claim 4
Dependent Claim
52 words
The modulator of claim 1, wherein the first center frequency is substantially equal to zero Hz, so that FSK tones comprise a complex spectrum having a real portion and an imaginary portion, and wherein said means for frequency shifting the filtered signal shift in into the frequency spectrum of the output signal.
Claim 5
Dependent Claim
18 words
The modulator of claim 3, wherein the filter has a band pass frequency range that includes zero Hz.
Claim 6
Dependent Claim
182 words
A modulator for modulating data in a modem, producing an output signal conveying the data over a data channel at a data rate, said modulator comprising: edge detection means, connected to receive the data that is to be modulated, for detecting an edge at which the data change state and producing an edge detect signal in response thereto, said change in state occurring when the data change between logic levels; and interpolation means, coupled to receive the edge detect signal and the data that are to be modulated, for sampling the data at a predefined sample rate and modulating a FSK signal having upper and lower frequencies centered about a first frequency in response to the logic levels of the data, said upper frequency corresponding to one logic level and said lower frequency corresponding to a different logic level, the logic level used to modulate the FSK signal being determined by the interpolation means as a function of the edge detect signal to increase the resolution with which the FSK signal is modulated by the data, thereby minimizing jitter in said signal.
Claim 7
Dependent Claim
182 words
A modulator for modulating data in a modem, producing an output signal conveying the data over a data channel at a data rate, said modulator comprising: edge detection means, connected to receive the data that is to be modulated, for detecting an edge at which the data change state and producing an edge detect signal in response thereto, said change in state occurring when the data change between logic levels; and interpolation means, coupled to receive the edge detect signal and the data that are to be modulated, for sampling the data at a predefined sample rate and modulating a FSK signal having upper and lower frequencies centered about a first frequency in response to the logic levels of the data, said upper frequency corresponding to one logic level and said lower frequency corresponding to a different logic level, the logic level used to modulate the FSK signal being determined by the interpolation means as a function of the edge detect signal to increase the resolution with which the FSK signal is modulated by the data, thereby minimizing jitter in said signal.
Claim 8
Dependent Claim
61 words
The modulator of claim 5, further comprising: a filter having an input that is coupled to the interpolation means to receive the FSK signal, said filter substantially attenuating frequencies outside a predetermined bandwidth, producing a filtered FSK signal; and means for frequency shifting the center frequency of the FSK signal so that it is within a bandwidth of the data channel.
Claim 9
Dependent Claim
29 words
The modulator of claim 5, further comprising: a digital-to-analog converter (DAC) that has an input coupled to receive the FSK signal, and which produces a corresponding analog FSK signal.
Claim 10
Dependent Claim
32 words
The modulator of claim 7, further comprising: a post filter having an input coupled to receive the analog FSK signal, producing a filtered analog FSK signal that is output from the modulator.
Claim 11
Dependent Claim
62 words
The modulator of claim 5, wherein the interpolation means comprise a timer and wherein the edge detect signal causes a then current time on the timer to be retained, so that the interpolation mean can determine a time interval since a previous sample interrupt occurred, each sample interrupt occurring at times spaced apart by a sample interval defined by the sample rate.
Claim 12
Dependent Claim
88 words
The modulator of claim 9, wherein the interpolation means further comprise a processor that interpolates the time during the sample interval at which the edge detect signal indicated a change in the logic level of the data based upon the current time at which the edge detect signal cause the current time on the timer to be retained, thereby improving the resolution with which such changes modulate the FSK signal and reducing jitter on it, by more accurately determining an incremental change in phase of the FSK signal.
Claim 13
Dependent Claim
43 words
The modulator of claim 5, further comprising an input latch that has an input connected to receive the data and an output coupled to the interpolation means, the data latch temporarily storing the input data while it is sampled by the interpolation means.
Claim 14
Dependent Claim
30 words
The modulator of claim 5, wherein the data are coupled asynchronously to the interpolation means and the data rate is variable, with a maximum value in excess of 1,500 baud.