SAA7108AE Datasheet, PDF (70/208 Pages) NXP Semiconductors – HD-CODEC

NXP Semiconductors
SAA7108AE; SAA7109AE
HD-CODEC
Other amplifications have to be normalized by using the following BCS control circuitry. In
these cases the prescaler has to be set to an overall gain of ≤ 1, e.g. for an accumulation
sequence of ‘1 + 1 + 1’ (XACL[5:0] = 2 and XC2_1 = 0), XDCG[2:0] must be set to ‘010’,
this equals ¹â„₄ and the BCS has to amplify the signal to ⁴⁄₃ (SATN[7:0] and CONT[7:0]
value = lower integer of ⁴⁄₃ × 64).
The use of XACL[5:0] is XPSC[5:0] dependent. XACL[5:0] must be < 2 × XPSC[5:0].
XACL[5:0] can be used to find a compromise between bandwidth (sharpness) and alias
effects.
Remark: Due to bandwidth considerations XPSC[5:0] and XACL[5:0] can be chosen
differently to the previously mentioned equations or Table 25, as the horizontal phase
scaling is able to scale in the range from zooming up by factor 3 to downscaling by a factor
of ¹⁰²⁴⁄₈₁₉₁.
Figure 38 and Figure 39 show some resulting frequency characteristics of the prescaler.
Table 25 shows the recommended prescaler programming. Other programming, other
than given in Table 25, may result in better alias suppression, but the resulting DC gain
amplification needs to be compensated by the BCS control, according to the equation:
CONT [7:0] = SATN [7:0] = lower integer of -_D----^2C---^X---^D-_g---^C_a---^G_i--_n--^[-²--_×-^:--⁰--₆^]---₄-
Where:
• 2^XDCG[2:0] ≥ DC gain
• DC gain = [(XACL[5:0] − XC2_1) + 1] × (XC2_1 + 1)
For example, if XACL[5:0] = 5, XC2_1 = 1, then the DC gain = 10 and the required
XDCG[2:0] = 4.
The horizontal source acquisition timing and the prescaling ratio is identical for both the
luminance path and chrominance path, but the FIR filter settings can be defined differently
in the two channels.
Fade-in and fade-out of the filters is achieved by copying an original source sample each
as first and last pixel after prescaling.
Figure 36 and Figure 37 show the frequency characteristics of the selectable FIR filters.
Table 24. FIR prefilter functions
PFUV[1:0] A2h[7:6] and
PFY[1:0] A2h[5:4]
Luminance filter coefficients
00
bypassed
01
121
10
−1 1 1.75 4.5 1.75 1 −1
11
12221
Chrominance coefficients
bypassed
121
3 8 10 8 3
12221
SAA7108AE_SAA7109AE_3
Product data sheet
Rev. 03 — 6 February 2007
© NXP B.V. 2007. All rights reserved.
70 of 208