720p Systems
Progressive Analog Component Video
Analog component signals are comprised of three signals, analog R′G′B′ or YPbPr. Referred to as 720p (since there are typically 720 active scan lines per frame and they are progressive), the frame rate is usually 59.94 Hz (60/1.001) to simplify the generation of (M) NTSC video. The analog interface uses 750 lines per frame, with active video present on lines 26–745, as shown in Figure 3.26.
FIGURE 3.26. 720p Vertical Interval Timing.
For the 59.94 Hz frame rate, each scan line time (H) is about 22.24 μs. Detailed horizontal timing is dependent on the specific video interface used, as discussed in Chapter 4.
Progressive Digital Component Video
SMPTE 296M specifies the representation for 720p digital R′G′B′ or YCbCr signals. Active resolutions defined within SMPTE 296M, their 1×Y and R′G′B′ sample rates (Fs), and frame rates, are:
| 1280×720p | 74.176 MHz | 23.976 Hz |
| 1280×720p | 74.250 MHz | 24.000 Hz |
| 1280×720p | 74.250 MHz | 25.000 Hz |
| 1280×720p | 74.176 MHz | 29.970 Hz |
| 1280×720p | 74.250 MHz | 30.000 Hz |
| 1280×720p | 74.250 MHz | 50.000 Hz |
| 1280×720p | 74.176 MHz | 59.940 Hz |
| 1280×720p | 74.250 MHz | 60.000 Hz |
Note that square pixels and a 16:9 aspect ratio are used. Example relationships between the analog and digital signals are shown in Figures 3.27 and 3.28, and Table 3.1. The H (horizontal blanking), V (vertical blanking), and F (field) signals are as defined in Figure 3.29.
FIGURE 3.27. 720p Analog-Digital Relationship (16:9 Aspect Ratio, 59.94 Hz Frame Rate, 74.176 MHz Sample Clock and 60 Hz Frame Rate, 74.25 MHz Sample Clock).
FIGURE 3.28. General 720p Analog-Digital Relationship.
Table 3.1. Various 720p Analog-Digital Parameters for Figure 3.28
| Active Horizontal Samples | Frame Rate (Hz) | 13 Y Sample Rate (MHz) | Total Horizontal Samples (A) | Horizontal Blanking Samples (B) | C Samples |
|---|---|---|---|---|---|
| 1280 | 24/1.001 | 74.25/1.001 | 4125 | 2845 | 2585 |
| 24 | 74.25 | 4125 | 2845 | 2585 | |
| 251 | 48 | 1536 | 256 | 21 | |
| 251 | 49.5 | 1584 | 304 | 25 | |
| 25 | 74.25 | 3960 | 2680 | 2420 | |
| 30/1.001 | 74.25/1.001 | 3300 | 2020 | 1760 | |
| 30 | 74.25 | 3300 | 2020 | 1760 | |
| 50 | 74.25 | 1980 | 700 | 440 | |
| 60/1.001 | 74.25/1.001 | 1650 | 370 | 110 | |
| 60 | 74.25 | 1650 | 370 | 110 |
Note: 1. Useful for CRT-based 50 Hz HDTVs based on a 31.250 kHz horizontal frequency. Sync pulses are −300 mV bi-level, rather than ±300 mV tri-level. 720p content scaled vertically to 1152i active scan lines; 1250i total scan lines instead of 750p.
FIGURE 3.29. 720p Digital Vertical Timing (720 Active Lines). V changes state at the EAV sequence at the beginning of the digital line. Note that the digital line number changes state prior to the start of horizontal sync, as shown in Figures 3.27 and 3.28.
