TDA8295 Datasheet, PDF (25/77 Pages) NXP Semiconductors – Digital global standard low IF demodulator for analog TV and FM radio

NXP Semiconductors
TDA8295
Digital global standard low IF demodulator for analog TV and FM radio
Table 17. PC_PLL_THRES register (address 05h) bit description
Legend: * = default value.
Bit Symbol
Access Value Description
7 to 4 -
R/W -
not used
3 to 0 PH_ERR_THRES[3:0] R/W
When the settable threshold for the linear phase
detector as part of the picture carrier PLL is
passed, the phase detector slope is weighted
according to the settings in PHASE_GAIN. This
feature is of advantage during adverse field
conditions. In case multipath happens like
ghosts, the PC PLL should not follow the sudden
phase jumps. So, the PC PLL is made slow
(lower loop bandwidth) with PC_PLL_THRES
after surpassing the threshold. This threshold is
related to a fraction of FS. There, FS is 90° if
PHASE_PER is logic 0 (default) or 180° when
logic 1. If the ICPM or ICFM is large because of
bad transmitters with oscillator pulling or
modulator imbalance, the PC PLL should follow
as true as possible. This can be done by
increasing the loop bandwidth with overweighting
(see PHASE_GAIN, Table 18).
0001
0010
0100*
1000
1_{⁄32 FS}
1_{⁄16 FS}
1_{⁄8 FS}
1_{⁄4 FS}
Table 18. PC_PLL_WGT register (address 06h) bit description
Legend: * = default value.
Bit Symbol
Access Value
Description
7
PHASE_PER
R/W
By default, the linear phase detector transfer
function is repetitive in π. This allows a good
picture carrier overmodulation performance,
because the PC PLL doesn’t need to reacquire
the 180° phase modulation, caused by the
excessive AM index above m = 100 % (negative
residual picture carrier).
0*
π (needed for overmodulation)
1
2π
6 to 0 PHASE_GAIN[6:0] R/W
phase error weighting (adaptive loop speed), see
also PH_ERR_THRES in Table 17 for
explanation
000 0001
000 0010
000 0100
000 1000
001 0000*
× ¹â„₁₆
× ¹â„₈
× ¹â„₄
× ¹â„₂
flat (no weighting)
010 0000 × 2
100 0000 × 4
TDA8295_1
Product data sheet
Rev. 01 — 4 February 2008
© NXP B.V. 2008. All rights reserved.
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