THS7373IPWR datasheet(39/50 Pages) TI

39 / 50 page

THS7373

www.ti.com

SBOS506 – DECEMBER 2009

The THS7373 CVBS CVBS filter has a nominal

450-V/µs slew rate. This bypass supports 1080p60

corner (–3 dB) frequency at 9.5-MHz and a –1-dB

signals along with computer R’G’B’ signals up to

passband typically at 8.2 MHz. This 9.5-MHz filter is

QXGA or UWXGA resolution. This mode still uses the

ideal for CVBS NTSC, PAL, and SECAM composite

dc + shift functionality along with the transparent

video (CVBS) signals. The 9.5-MHz, –3-dB corner

sync-tip-clamp

function.

Essentially,

the

only

frequency was designed to achieve 54 dB of

difference in this mode is that the HD filters are

attenuation

MHz—a

common

sampling

bypassed.

frequency between the DAC/ADC second and third

Nyquist zones found in many video systems. This

BENEFITS OVER PASSIVE FILTERING

consideration is important because any signal that

Two key benefits of using an integrated filter system,

appears around this frequency can also appear in the

such as the THS7373, over a passive system are

baseband as a result of aliasing effects of an ADC

PCB area and filter variations. The small TSSOP-14

found in a receiver.

package for four video channels is much smaller over

The THS7373 HD filters have a nominal corner

a passive RLC network, especially a six-pole passive

(–3-dB) frequency at 36MHz and a –1-dB passband

network. Additionally, consider that inductors have at

typically at 33 MHz. This 36-MHz filter is ideal for HD

best ±10% tolerances (normally, ±15% to ±20% is

720p, 1080i, up to 1080p30 Y’/P’B/P’R, broadcast

common)

and

capacitors

typically

have

±10%

G’B’R’ signals, and computer R’G’B’ video signals.

tolerances. Using a Monte Carlo analysis shows that

The 36-MHz, –3-dB corner frequency was designed

the filter corner frequency (–3 dB), flatness (–1 dB), Q

to achieve 40 dB of attenuation at 74.25 MHz—a

factor (or peaking), and channel-to-channel delay

common sampling frequency between the DAC/ADC

have wide variations. These variances can lead to

second and third Nyquist zones found in many video

potential

performance

and

quality

issues

systems.

mass-production environments. The THS7373 solves

most of these problems with the corner frequency

Keep in mind that images do not stop at the DAC

being essentially the only variable.

sampling frequency, fS (for example, 27 MHz for

traditional CVBS DACs); they continue around the

Another concern about passive filters is the use of

sampling frequencies of 2x fS, 3x fS, 4x fS, and so on

inductors. Inductors are magnetic components, and

(that is, 54-MHz, 81-MHz, 108-MHz, etc.). Because of

are

therefore

susceptible

electromagnetic

these multiple images, an ADC can fold down into the

coupling/interference

(EMC/EMI).

Some

common

baseband signal, meaning that the low-pass filter

coupling can occur because of other video channels

must also eliminate these higher-order images. The

nearby using inductors for filtering, or it can come

THS7373 filters are Butterworth filters and, as such,

from nearby switched-mode power supplies. Some

do not bounce at higher frequencies, thus maintaining

other forms of coupling could be from outside sources

good attenuation performance.

with strong EMI radiation and can cause failure in

EMC testing such as required for CE compliance.

The filter frequencies were chosen to account for

process variations in the THS7373. To ensure the

One concern about an active filter in an integrated

required video frequencies are effectively passed, the

circuit is the variation of the filter characteristics when

filter corner frequency must be high enough to allow

the ambient temperature and the subsequent die

component variations. The other consideration is that

temperature

change.

minimize

temperature

the attenuation must be large enough to ensure the

effects,

the

THS7373

uses

low-temperature

anti-aliasing/reconstruction filtering is sufficient to

coefficient resistors and high-quality, low-temperature

meet the system demands. Thus, the selection of the

coefficient capacitors found in the BiCom3X process.

filter frequencies was not arbitrarily selected and is a

These filters have been specified by design to

good compromise that should meet the demands of

account for process variations and temperature

most systems.

variations to maintain proper filter characteristics.

This approach maintains a low channel-to-channel

HD FILTER BYPASS MODE

time delay that is required for proper video signal

performance.

The THS7373 has an HD filter bypass mode that

bypasses the HD channels internal filters, thus the

THS7373 effectively becomes a fixed gain 2-V/V

operational amplifier. Bypassing the HD filters results

in an amplifier supporting a 350-MHz bandwidth and

Submit Documentation Feedback

Product Folder Link(s): THS7373

THS7373IPWR Datasheet(PDF) 39 Page - Texas Instruments

THS7373IPWR Datasheet(HTML) 39 Page - Texas Instruments

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

Datasheet Download

Link URL