Signal limiting apparatus having improved spurious signal performance and methods
First Claim
1. A limiter apparatus for amplitude limiting an input information signal having a plurality of frequency components, comprising:
- means for filtering said input signal, said means having a low pass frequency response for providing at a first output selected low frequency components in said input signal and having a high pass frequency response for providing at a second output selected higher frequency components present in said input signal;
controllable attenuating means coupled to said second output for selectively attenuating said high frequency components according to the value of a control signal applied thereto;
combining means responsive to an output of said attenuating means and said first output of said filtering means for providing at an output a combined signal; and
limiting means responsive to said combined signal to limit the magnitude of said combined signal according to a first threshold value and for providing said control signal for said attenuating means for controlling said attenuation of said high frequency components according to the extent of limiting whereby said limiter apparatus operates to provide reduced spurious frequencies for those higher frequencies contained within said input signal as compared to said lower frequency components.
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Abstract
A limiter circuit responds to an input signal which has a plurality of frequencies within a given band. The input signal is split up into two frequency ranges by means of a low pass filter for one range and a high pass filter for a second range. The output of the low pass filter is directed to a first limiter while the output of the high pass filter is directed to a variable notch filter. The outputs from the first limiter and the notch filter are added together to provide a sum signal. The sum signal is applied to a second limiter which performs limiting strictly according to the amplitude. The outputs of the second limiter signal provide the desired signal and a control signal to determine how often the second limiter is limiting. The control signal varies the attenuation of the notch filter. In this manner frequencies, within a selective range and which will be otherwise effected by the spurious frequencies generated during limiting, are reduced.
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Citations
19 Claims
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1. A limiter apparatus for amplitude limiting an input information signal having a plurality of frequency components, comprising:
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means for filtering said input signal, said means having a low pass frequency response for providing at a first output selected low frequency components in said input signal and having a high pass frequency response for providing at a second output selected higher frequency components present in said input signal; controllable attenuating means coupled to said second output for selectively attenuating said high frequency components according to the value of a control signal applied thereto; combining means responsive to an output of said attenuating means and said first output of said filtering means for providing at an output a combined signal; and limiting means responsive to said combined signal to limit the magnitude of said combined signal according to a first threshold value and for providing said control signal for said attenuating means for controlling said attenuation of said high frequency components according to the extent of limiting whereby said limiter apparatus operates to provide reduced spurious frequencies for those higher frequencies contained within said input signal as compared to said lower frequency components. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
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14. A method of limiting an information signal, comprising the steps of:
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filtering said signal to provide a first band of low frequencies contained in said information signal at a first output and to provide a second band of high frequencies in said signal at a second output; limiting said first band of frequencies; controllably attenuating said second band of frequencies; combining said limited first band with said attenuated second band to provide a combined signal; limiting said combined signal to provide an output combined signal; and controlling the amount of attenuation according to the extent of limiting of said combined signal. - View Dependent Claims (15, 16, 17, 18, 19)
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Specification