OPA361-Q1

SBOS552

– MARCH 2011

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Figure 5. Multiburst Signal (CCIR 18/1) Shows Very Flat Frequency Response

The CCIR17 test pattern contains a 2T and a 20T pulse, as shown in Figure 6. The 2T pulse is used to check for

pulse distortion and reflection, and the 20T pulse is used to check for amplitude and group delay between

chrominance and luminance. Neither pulse exhibits any distortion or group delay artifacts.

Figure 6. CCIR 17 2T and 20T Pulses Show No Visible Distortion

INTERNAL LEVEL SHIFT

Many common video DACs embedded in digital media processors, like the new OMAP242x processors, operate

on a single supply (no negative supply). Typically, the lowest point of the sync pulse output by these video DACs

is close to 0V. With a 0V input, the output of a common single-supply op amp saturates at a voltage

> 0V. This

effect would clip the sync pulse, and therefore degrade the video signal integrity. The OPA361-Q1 employs an

internal level shift circuit to avoid clipping. The input signal is typically shifted by approximately 11mV. This shift

is well within the linear output voltage range of the OPA361-Q1 with a standard 150

Ω video load.

Output Swing Capability

Figure 7 shows the true output swing capability of the OPA361-Q1 by taking the tip of the input sync pulse to a

slightly negative voltage. Even when the output sync tip is at 3mV, the output after the 75

Ω series termination still

shows no clipping of the sync pulse.

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