OPA360 Datasheet, PDF (8/24 Pages) Burr-Brown (TI) – 3V Video Amplifier with 6dB Gain and Filter in SC70

OPA360
SB0S294E − DECEMBER 2003 − REVISED SEPTEMBER 2006
FREQUENCY RESPONSE OF THE OPA360
Frequency response measurements evaluate the ability of
a video system to uniformly transfer signal components of
different frequencies without affecting their respective
amplitudes. Figure 3 shows the multiburst test pattern;
Figure 4 shows the multipulse. The top waveforms in
these figures show the full test pattern. The middle and
bottom waveform are a more detailed view of the critical
portion of the full waveform. The middle waveform
represents the input signal from the video generator; the
bottom waveform is the OPA360 output to the line.
www.ti.com
Chrominance-to-luminence gain inequality (or relative
chrominance level) is a change in the gain ratio of the
chrominance and luminence components of a video
signal, which are at different frequencies. A common test
pattern is the pulse in test pattern CCIR 17, shown in
Figure 5. As in Figure 3 and Figure 4, the top waveform
shows the full test pattern; the middle and bottom
waveform are a more detailed view of the critical portion of
the full waveform, with the middle waveform representing
the input signal from the video generator and the bottom
waveform being the OPA360 output to the line.
Figure 3. Multiburst (CCIR 18) Test Pattern (PAL)
Figure 4. Multipulse Test Pattern (PAL)
8
Figure 5. CCIR 17 Test Pattern (PAL)
Gain errors most commonly appear as attenuation or
peaking of the chrominance information. This shows up in
the picture as incorrect color saturation. Delay distortion
will cause color smearing or bleeding, particularly at the
edges of objects in the picture. It may also cause poor
reproduction of sharp luminence transitions.
All waveforms in Figure 3 through Figure 5 were taken
using the sag correction feature of OPA360. Figure 3
through Figure 5 show that the OPA360 causes no visible
distortion or change in gain throughout the entire video
frequency range.
INTERNAL LEVEL SHIFT
Many common video DACs embedded in digital media
processors like TI’s TMS320DM270 and the new
OMAP2420 processors operate on a single supply (no
negative supply). Typically, the lowest point of the sync
pulse output by these Video DACs corresponds to 0V. With
a 0V input, the output of common single-supply op amps
saturates at a voltage > 0V. This effect would clip the tip of
the sync pulse and therefore degrade the video signal
integrity. The OPA360 employs an internal level shift circuit
to avoid clipping. The input signal is typically shifted by