TMC22091 datasheet(45/60 Pages) CADEKA

45 / 60 page

PRODUCT SPECIFICATION

TMC22091/TMC22191

Filtering

The TMC22x91 incorporates internal digital ﬁlters to estab-

lish appropriate bandwidths and simplify external analog ﬁl-

ter designs.

Color-Difference Low-Pass Filters

The color-difference low-pass ﬁlters in the TMC22x91

establish chrominance bandwidths which meet the speciﬁca-

tions outlined in CCIR Report 624-3, Table II, Item 2.6, for

system I over a range of pixel rates from 12.27 Mpps to

14.75 Mpps. Equal bandwidth is established for both color-

difference channels.

Figure 26. Color-Difference Low-Pass Filter Response

Interpolation Filters

The Chroma Modulator output and the luminance data path

are digitally ﬁltered with sharp-cutoff low-pass interpolation

ﬁlters. These ﬁlters ensure that aliased subcarrier, chromi-

nance, and luminance frequencies are sufﬁciently suppressed

in the frequency band above base-band video and below the

pixel frequency (fS/4 to 3fS/4, where fS is the PXCK

frequency).

-10

-20

-30

Frequency (MHz)

-40

-50

-60

-70

-80

-90

24363A

f = 14.27 Mpps

CCIR Rep 624 Specification

f = 12.27 Mpps

Since these are ﬁxed-coefﬁcient digital ﬁlters, their ﬁlter

characteristics depend upon clock rate. Figures 26 and 27

show the frequency response for two pixel rates, 12.27 MHz

and 14.75 MHz.

Figure 27. Chroma Modulator and Luminance

Interpolation Filter Full Spectrum Response

Figure 28. Chroma Modulator and Luminance

Interpolation Filter Passband Detail

All digital-to-analog reconstruction systems exhibit a high

frequency roll-off as a result of the zero-order hold charac-

teristic of D/A converters. This response is commonly

referred to as a sin(x)/x response. It is a function of the sam-

pling rate of the output D/A.

-10

-20

-30

Frequency (MHz)

-40

-50

-60

-70

-80

-90

24394A

f = 14.75 Mpps

f = 12.27 Mpps

-1

-2

-3

Frequency (MHz)

-4

24365A

f = 14.75 Mpps

f = 12.27 Mpps

Figure 25. Frequency/Phase Data Transfer

PXCK

PIXEL

24383A

FREQUENCY

PHASE

FIELD IDENTIFICATION

PIXEL

FID f23:20 f19:16 f15:12 f11:8 f7:4

f3:0 φ23:20 φ19:16 φ15:12 φ11:8 φ7:4 φ3:0

GHSYNC

CVBS7-0

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