Up-conversion mechanism employing side lobe-selective pre-distortion filter and frequency replica-selecting bandpass filter respectively installed upstream and downstream of digital-to-analog converter
First Claim
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1. A method of up-converting a baseband signal having a given bandwidth to an output signal having said given bandwidth centered at a prescribed center frequency higher than that of said baseband signal comprising the steps of:
- (a) providing said baseband signal as a sampled input baseband signal;
(b) providing a digital-to-analog converter that is operative to convert a sampled signal supplied thereto into an analog signal having a spectral content containing distorted replicas of the frequency content of said sampled signal at successively adjacent spaced-apart center frequencies;
(c) modifying a prescribed frequency content of said sampled input baseband signal in accordance with a pre compensation mechanism that is operative to pre-distort said sampled baseband signal into a pre-distorted sampled baseband signal, such that processing of said pre-distorted sampled baseband signal by means of the digital-to-analog converter provided in step (b) produces an analog output signal having a spectral content of said sampled baseband signal at successively adjacent spaced-apart center frequencies, but with a selected normally distorted replica thereof other than in a main lobe of said baseband signal, and containing said given bandwidth centered at said prescribed center frequency higher than that of said baseband signal compensated by said pre-compensation mechanism;
(d) coupling said pre-distorted sampled baseband signal as modified in step (c) to said digital-to-analog converter, so as to produce said analog output signal in which said selected replica of the frequency content of said sampled baseband signal has been compensated by said pre-compensation mechanism; and
(e) subjecting the analog output signal produced in step (d) to a bandpass filtering operation which produces a bandpass-filtered analog output signal having a frequency content that is limited to said selected replica of the frequency content of said baseband signal at said prescribed center frequency.
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Abstract
An up-converter for digitally sampled baseband signals takes advantage of the sinc(x) spectral replication functionality of a DAC, using a post-DAC, band pass filter to isolate a baseband replica that falls within that sidelobe of the DAC'"'"'s sinc(x) frequency response containing the desired IF. The parameters of a pre-compensation filter and the gain of a post DAC amplifier are set to compensate for the distortion and attenuation imparted by the DAC'"'"'s sinc(x) frequency response.
97 Citations
19 Claims
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1. A method of up-converting a baseband signal having a given bandwidth to an output signal having said given bandwidth centered at a prescribed center frequency higher than that of said baseband signal comprising the steps of:
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(a) providing said baseband signal as a sampled input baseband signal; (b) providing a digital-to-analog converter that is operative to convert a sampled signal supplied thereto into an analog signal having a spectral content containing distorted replicas of the frequency content of said sampled signal at successively adjacent spaced-apart center frequencies; (c) modifying a prescribed frequency content of said sampled input baseband signal in accordance with a pre compensation mechanism that is operative to pre-distort said sampled baseband signal into a pre-distorted sampled baseband signal, such that processing of said pre-distorted sampled baseband signal by means of the digital-to-analog converter provided in step (b) produces an analog output signal having a spectral content of said sampled baseband signal at successively adjacent spaced-apart center frequencies, but with a selected normally distorted replica thereof other than in a main lobe of said baseband signal, and containing said given bandwidth centered at said prescribed center frequency higher than that of said baseband signal compensated by said pre-compensation mechanism; (d) coupling said pre-distorted sampled baseband signal as modified in step (c) to said digital-to-analog converter, so as to produce said analog output signal in which said selected replica of the frequency content of said sampled baseband signal has been compensated by said pre-compensation mechanism; and (e) subjecting the analog output signal produced in step (d) to a bandpass filtering operation which produces a bandpass-filtered analog output signal having a frequency content that is limited to said selected replica of the frequency content of said baseband signal at said prescribed center frequency. - View Dependent Claims (2, 3, 4)
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5. A signal processing apparatus for up-converting a digitally sampled baseband signal having a given bandwidth to an analog output signal having said given bandwidth centered at a prescribed center frequency higher than that of said digital baseband signal comprising:
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an input signal port to which said digitally sampled baseband signal is applied; a digital-to-analog converter that is operative to convert a sampled signal supplied thereto into an analog signal having a spectral content containing distorted replicas of the frequency content of said sampled signal at successively adjacent spaced-apart center frequencies; a pre-compensation filter installed between said input signal port and said digital-to-analog converter and being operative to pre-distort said digitally sampled baseband signal into a pre-distorted digitally sampled baseband signal, such that processing of said pre-distorted digitally sampled baseband signal by said digital-to-analog converter produces an analog output signal having a spectral content of said digitally sampled baseband signal at successively adjacent spaced-apart center frequencies, but with a selected normally distorted replica thereof, other than in a main lobe of said baseband signal, and containing said given bandwidth centered at said prescribed center frequency higher than that of said baseband signal compensated by said pre-compensation mechanism; and a bandpass filter which is coupled to receive said analog output signal produced by said digital-to-analog converter and produces a bandpass-filtered analog output signal having a frequency content that is limited to that of said selected replica of the frequency content of said baseband signal at said prescribed center frequency. - View Dependent Claims (6, 7, 8, 13, 14, 15, 16, 17, 18, 19)
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- 9. An up-converter for a sampled baseband signal, said up-converter comprising a digital-to-analog converter having a frequency domain distortion function, a pre-compensation filter, having an input to which said sampled baseband signal is coupled, and an output coupled to said digital-to-analog converter, said pre-compensation filter having a transfer function that compensates for distortion of a selected portion of said frequency of said frequency domain distortion function containing a desired IF frequency, other than a main lobe of said baseband signal, and a bandpass filter to which the analog output of said digital-to-analog converter is coupled, said bandpass filter having a passband that isolates a selected replica of the frequency content of said baseband signal at said desired IF frequency.
Specification