The present invention relates to a technique for clipping burst complex signal. The technique can be applied to both digital or analog signals. The in phase “I” and the quadrature phase “Q” of the complex signal are clipped without changing the phase of the complex signal. The clipping can be applied to bursty complex signals as well as real signal. In the case of real signal the quadrature “Q” component is zero. The clipping is based on rolling average, instantaneous value of the amplitude of the complex signal as well as absolute value of the rolling average of amplitude. In any wireless communication system one of the critical components is the power amplifier. This component has a major contribution in cost, power consumption, and size of the system. The main reason is the requirement of wireless radio communication system for linear power amplifiers. The higher the linearity, the higher the power consumption, cost and size. In order to minimize the cost, size and power consumption there is a need for techniques that overcome this problem. This invention conquers these challenges by using a simple and accurate peak suppression using a novel amplitude clipping technique.
According to the invention, an amplitude clipping technique, used for bursty complex and real signals, uses a plurality of simple and accurate circuits in conjunction with intelligent signal processing to reduce the peak to average ratio without disturbing the properties of the complex or real signal. By intelligent, it is meant that amplitude clipping has features of adaptability to the input samples, such as ability to consider the changes due to average and instantaneous value of the complex or real signal. The amplitude clipping can be applied to complex baseband and real IF or RF signal. The conditioning or amplitude clipping helps to decrease the signal crest factor or peak to average ratio and ease the linearity requirements for various circuits that the signal is applied to. The conditioning is based amplitude clipping using the rolling average and instantaneous value of the signal. The input to the amplitude clipping circuit or function should be within a limit that can be handled by the circuit or function.
In a particular embodiment, amplitude clipping circuit or function comprises a rolling average calculation, an instantaneous value calculation, a look up table containing the clipping value, multipliers, and low pass filter. The rolling average calculates the average of the complex or real signal. The look up table takes the rolling average and the instantaneous of the signal to define the amount of clipping and the clipping multiplier factor. The multiplier take the output of the look up table and multiply by the real signal or the in phase “I” and quadrature “Q” of the complex signal. The clipped real and complex signal are then filtered to remove the unwanted signals. In case of the complex signal the “I” and “Q” signals are individually filtered. When the signal is real the filtering is at the frequency of the signal whether baseband, or higher frequency. If it is not baseband then the filter is a band pass filter.
The invention will be better understood by reference to the following detailed description in conjunction with the accompanying drawings.
In a first preferred embodiment of the invention the amplitude clipping function uses the rolling average and the instantaneous of the amplitude of the complex signal to be used by a look up table. In a second embodiment the look up table uses the rolling average and the instantaneous value of the amplitude of the complex signal to define the amount of the clipping of the complex signal. In a third embodiment the look up table also uses the absolute value of the amplitude rolling average to determining the clipping amount. In a fourth embodiment the amplitude clipping factor is multiplied with the “I” and “Q” of the complex signal to avoid any phase distortion. In a fifth embodiment the clipped “I” and “Q” signals are low pass filtered to remove the unwanted signals from the amplitude clipped complex signal. In a sixth embodiment the low pass filter bandwidth is higher or equal to the Nyquist bandwidth times one plus the roll off factor of the original baseband filter used to filter the “I” and “Q” signals. In a seventh embodiment the instantaneous of the signal amplitude is used to determine the presence of the burst. In an eight embodiment the instantaneous of the signal amplitude is used to determine the presence of the bust is with some programmable delay depending on the number of the samples per symbol. In a ninth embodiment an alternative amplitude clipping solution calculates the instantaneous amplitude and phase of the complex signal. In a tenth embodiment the instantaneous phase of the signal stays unchanged and the instantaneous amplitude of the signal is clipped if exceeds a predefined threshold. In an eleventh embodiment the complex signal is reconstructed using it phase and clipped amplitude, if the signal is not clipped then the original signal is used. In a thirteenth embodiment the clipped “I” and “Q” signal are low pass filtered to remove unwanted signals. In a fourteenth embodiment a real signal is when the “Q” component of the complex signal does not exist and signal could be at baseband or at a higher frequency.
Referring to
1. Calculate the rolling average of the amplitude of the transmitter baseband output 100.
2. Calculate the instantaneous value of the amplitude of the transmitter baseband output 100.
3. Calculate the ratio of the instantaneous and rolling average of the complex signal amplitude.
4. Calculate the instantaneous phase of the transmitter baseband output 100.
5. Calculates the amount of the amplitude clipping of the transmitter baseband output 100.
6. Use a look up table to find the clipping amount based on ratio of the instantaneous and absolute value of the rolling average of the signal amplitude as well as absolute value of the rolling average of the amplitude.
7. Use a programmable delay to establish the presence and absence of the burst of complex or real signal.
8. Clip the amplitude of the transmitter output 100.
9. Filter the clipped “I” and “Q” signals to remove unwanted signals
10. Have a low pass filter with a bandwidth equal or higher than Nyquist bandwidth times one plus the roll off the original baseband filter.