Samsung S5PC110, Manual

Page: 1490 / 2426

S5PC110_UM 7 6BTVOUT & VIDEO DAC
7-18
7.9 OVERSAMPLING & DAC COMPENSATION FILTER (OSF MODULE)
The TVOUT module provides 2x or 4X oversampling filter prior to DAC in order to ease the design of analog anti-
image filter circuitry. For interlaced scanning case whose sample rate is 13.5MHz, four times oversampling
provides the final output sampling rate as 54Msps (samples per second). For progressive scanning with double
sample rate, 27MHz, OSF module performs two times oversampling with the result of also 54Msps.
The DAC has high frequency attenuation which comes from the sin(x)/x characteristic of sample-and-hold nature
and can have more attenuation for some specific reasons. As OSF has enough number of taps with
programmable coefficients, compensation of such attenuation is done by making the filter response to boost at
high frequency.
OSF operates in different ways according to the oversampling ratio; the number of taps and the meanings of the
coefficient registers are different for each case.
4x oversampling case: 13.5Msps interlaced mode. It operates as 4-polyphase 95-tap FIR filters. All the coefficient
registers (SDO_OSFC00_0~SDO_OSFC23_0<DAC #0>, SDO_OSFC00_1~SDO_OSFC23_1<DAC #1>,
SDO_OSFC00_2~SDO_OSFC23_2<DAC #2>) are used.
2x oversampling case: 27Msps progressive mode. It operates as 2-polyphase 47-tap FIR filter. Half of the filter
coefficient registers (SDO_OSFC12_0~SDO_OSFC23_0<DAC #0>, SDO_OSFC12_0~SDO_OSFC23_0<DAC
#1>, SDO_OSFC12_2~SDO_OSFC23_2<DAC #2>,) are used. The remaining values should be set to zero.
The target filter should be a centre symmetric, that is,
Let h(i) a filter coefficient whose index is i.
N is odd number. (For 4x, N = 95 and for 2x, N=47)
h(i) = h(N-i) for i=0~[N/2]-1, where [] means rounding to the nearest integers towards zero.