GC1115 Datasheet, PDF (25/80 Pages) Texas Instruments – Crest Factor Reduction Processor

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GC1115
SLWS144 – FEBRUARY 2005
Figure 9. Typical Symmetric Cancel Pulse Impulse Response, CANCEL_DELAY = 50
It is possible, however, to generate cancellation pulses whose largest coefficient is less than CAN-
CEL_LENGTH/2. Such cancellation pulses are called minimum phase pulses. Minimum-phase cancellation
pulses reduce the effective delay through the GC1115. Figure 10 illustrates the impulse response of a minimum
phase cancellation pulse. Notice that the largest magnitude coefficient (tap 7) is significantly closer to tap 1 than
to the middle coefficient (tap 25). The GC1115 can use either non-minimum phase or minimum phase
cancellation pulses. If a non-minimum phase filter is being used, CANCEL_DELAY = CANCEL_LENGTH / 2. If a
minimum phase filter is being used, CANCEL_DELAY < CANCEL_LENGTH / 2. CANCEL_DELAY must be
properly initialized to compensate for the cancellation pulse delay.
Figure 10. Minimum Phase Cancel Pulse Impulse Response, CANCEL_DELAY = 7
Software Timer
The GC1115 provides a flexible, user-controlled software timer that can serve as a programmable
synchronization source. The timer is controlled through the TIMER_SYNC register, which allows users to select
the event that triggers the timer. Before enabling the timer to start (via the TIMER_CTL register), the user
specifies a timer period using the TIMER_HI_RST and TIMER_LO_RST registers. The timer is decremented with
each internal clock edge (normally at a frequency of 4 x IN_CLK). When the TIMER_SYNC event occurs, the
timer copies the 32-bit values contained in TIMER_HI_RST and TIMER_LO_RST into a GC1115-internal 32-bit
timer register. This 32-bit timer is then decremented with each internal chip clock (normally chip clock = 4 x
IN_CLK). When the timer reaches zero, the timer is re-loaded from TIMER_HI_RST and TIMER_LO_RST
(periodic timer event), or the timer is disabled (for one-time timer events). Bit 15 of the TIMER_SYNC register
determines the timer mode (periodic or one-time).
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