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GC1115 Datasheet(PDF) 6 Page - Texas Instruments |
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GC1115 Datasheet(HTML) 6 Page - Texas Instruments |
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6 / 82 page  www.ti.com −4 −3 −2 −1 0 1 2 3 4 x 10 7 −20 0 20 40 60 80 100 Power spectral density: input (blue) & distortion (red) Distortion Spectrum, 8 dB Output PAR Distortion Spectrum, 5 dB Output PAR Input Spectrum SUMMARY OF GC1115 FEATURES GC1115 SLWS144C – FEBRUARY 2005 – REVISED JUNE 2006 The GC1115 reduces the amplitude of peaks in a way that keeps the out-of-band (ACLR) energy well below required levels. Users can determine how much in-band distortion is acceptable by monitoring the effects of peak cancellation at a given output PAR, using two key in-band distortion metrics for CDMA signals: 1. peak code domain error, or PCDE, and 2. composite error vector magnitude, or EVM Various CFR signal quality metrics (ACLR, PCDE, EVM, CCDF) will be further discussed in a subsequent section. Figure 5. Spectral View of Distortion Refer to the GC1115 functional block diagram for the following discussion. The GC1115 removes peaks from an input signal stream by subtracting user-designed, spectrally shaped cancellation pulses from detected peaks in the input waveform that are above a user-specified detection threshold. The cancellation pulse’s spectral shape matches that of the GC1115 input signal’s single- or multi-carrier configuration. This cancellation pulse design methodology ensures that energy is only added into frequency bands where signal energy is located, minimizing out-of-band energy that could otherwise increase ACLR/ACPR. Cancellation pulses may be real or complex. Real cancellation pulses are used when the input signal spectrum is symmetric, while complex cancellation pulses are used when the input signal spectrum is asymmetric. A single cancellation pulse reduces the peak amplitude of multiple samples around each signal peak while maintaining both the in-band (PCDE, cEVM) and out-of-band (ACLR) signal quality requirements. Peaks are cancelled to a user-specified level, which is called the output peak-to-average ratio, or PAR. The GC1115 provides four sequential peak detection and cancellation (PDC) stages to remove peaks. The PDC stage thresholds are normally set so that earlier stages remove the largest peaks, while later stages remove smaller, remaining peaks. 6 Submit Documentation Feedback |
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