GC1115_06 Datasheet, PDF (13/82 Pages) Texas Instruments – Crest Factor Reduction Processor

GC1115
www.ti.com
SLWS144C – FEBRUARY 2005 – REVISED JUNE 2006
CANCEL_MODE, CANCEL_LENGTH, CANCEL_DELAY, Cancellation Coefficients
The GC1115 applies user-specified cancellation coefficients to detected peaks. Cancellation coefficients can
contain either real or complex values, to support both symmetric and asymmetric input spectra. For this reason,
the CANCEL_MODE, CANCEL_LENGTH, and CANCEL_DELAY registers must be properly initialized before
the GC1115 begins processing input samples. The cancellation coefficients themselves (in either real or
complex format) must be copied to the GC1115 canceler RAMs in a two-step process:
• The microprocessor or FPGA writes the cancellation coefficients to memory-mapped shadow RAM registers
• The shadow RAM registers are copied to one or more (of a total of eight) cancellation pulse SRAMs after a
CANCEL_SYNC event occurs.
The CANCEL_MODE register determines whether the GC1115 is using real or complex coefficients
(corresponding to a symmetric or an asymmetric input spectrum), as well as whether coefficient symmetry is to
be exploited. Coefficient symmetry (mirrored coefficients) only applies when using real coefficients. The
CANCEL_MODE register also contains a four-bit field that indicates a timeout or hysteresis value. A non-zero
timeout value indicates that the PDCs are to examine the envelope of the input signal, rather than the magnitude
of the input signal. TI-provided Matlab cancel pulse design software automatically calculates the timeout value.
The CANCEL_LENGTH register specifies the number of unique cancellation coefficients used to cancel peaks.
The CANCEL_MODE register settings affect the interpretation of CANCEL_LENGTH. The following table
describes how CANCEL_LENGTH and CANCEL_DELAY are used, depending on CANCEL_MODE:
Table 2. Relationship Between CANCEL_MODE, CANCEL_LENGTH,
and CANCEL_DELAY
CANCEL_MODE
0 (Real, unique coefs)
1 (Real, mirrored coefs)
1 (Complex, unique coefs)
CANCEL_LENGTH
N (odd, from 15 to 255)
N (odd, from 15 to 255)
N (odd, from 15 to 127)
CANCEL_DELAY
(N-1)/2
N
(N-1)/2
OPERATING MODES
The GC1115 supports a variety of operating modes that accommodate a range of input formats, number of
channels, and follow-on A/D converter and transmit architectures. Users select a specific input and output
operating mode that depends upon:
• The number of channels (one or two)
• The input sampling rate:
– Up to 130 Msamp/sec in 1-channel mode
– Up to 65 Msamp/sec in 2-channel mode
– Down to 25 Msamp/sec in 1-channel parallel mode
– Down to 12.5 Msamp/sec in 1-channel multiplexed mode, or in 2-channel mode
• The input format (parallel or multiplexed)
• The input decimation factor (1 or 2)
• The output interpolator mode (bypass, 2x real, 2x complex, 4x real)
• The output format (parallel, multiplexed, or odd-even; real or complex)
• The internal GC1115 clock rate (up to 320 MHz)
• The PLL multiplier (1x, 2x, or 4x)
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