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THS8136 Datasheet(PDF) 5 Page - Texas Instruments |
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THS8136 Datasheet(HTML) 5 Page - Texas Instruments |
5 / 17 page Blanking Generation Sync Generation Device Configuration DAC Operation THS8136 www.ti.com ........................................................................................................................................................................................... SLES236 – NOVEMBER 2008 The BLANK control input forces the output amplitude on all channels to the blanking or reference level, irrespective of the value on the data input ports. The output blanking level on each channel and its relation to active video varies depending on the mode of operation. In generic DAC mode, the output blank level for each DAC is at 0 V and corresponds to a DAC input code of 0. When sync insertion is enabled a 350-mV dc bias (RFS selected for 700-mV output) is applied to provide room for bi-level sync insertion. When RGB sync insertion is enabled, the output blank level of each DAC will be at 350 mV and will correspond to a DAC input code of 0. In YPbPr video mode, the blank level of each DAC is 350 mV, but the AR and AB blank levels correspond to a DAC input code of 512 to accommodate mid-level UV blank levels. A video to blank level amplitude ratio of 2:1 is maintained for various RFS values, provided the maximum DAC output compliance is not exceeded. The SYNC and SYNC_T control inputs can be used to enable the superposition of a bi-level sync on the AG DAC output. Correctly timed assertion of the SYNC input (active low) allows insertion of an analog composite sync on the AG DAC output consisting of horizontal sync and vertical sync. The video to sync amplitude ratio is 7:3 providing a 300 mV sync tip, when FSADJ is selected to provide 700 mV full-scale graphics or video. This 7:3 video to sync amplitude ratio is maintained for various RFS values, provided the maximum DAC output compliance is not exceeded. The SYNC-T input pin must be connected to DVSS (or logic low) to enable sync insertion. The THS8136 operating mode is determined from the state of the SYNC, SYNC-T, M1, and M2 control terminals. Generic DAC mode is easily selected by connecting SYNC and SYNC_T to DVDD (or logic high) and M1 and M2 to DVSS (logic low). To enable sync insertion, the SYNC_T terminal must be connected to DVSS (or logic low). YPbPr video mode can be selected for support of mid-level PbPr blanking by connecting the sync control input to both the SYNC and M2 input terminals. The M1 terminal must be connected to DVSS (logic 0) for all operating modes. See Table 1 and Figure 4, Figure 5, and Figure 6 for additional information on configuring the THS8136. Table 1. Table 1. Device Configuration OPERATING MODE M1 M2 SYNC_T SYNC DESCRIPTION Sync insertion disabled. The blank level on all DAC outputs corresponds Generic DAC 0 0 1 1 to 0-V and DAC input code 0. DC bias and sync insertion enabled. The blank level on all DAC outputs RGB Sync Insertion 0 0 0 SYNC corresponds to DAC input code 0. DC bias and sync insertion enabled. AB and AR mid-level blanking YPbPr Sync Insertion 0 SYNC 0 SYNC corresponds to DAC input code 512. The DAC output drivers generate a current with a drive level that can be user-modified by choosing an appropriate resistor value RFS connected between the FSADJ terminal and AVSS (GND). All current source amplitudes (graphics/video, blanking, and sync on AG) are derived from RFS and an internal voltage reference such that the relative amplitudes of sync, blank, and graphics/video are always equal to their nominal relationships. The relative amplitudes of these current drivers are maintained without regard to the value of RFS, as long as the maximum current drive capability is not exceeded. Figure 3 shows the relationship between RFS and the current drive level on each channel for full-range DAC input. The voltage compliance outputs in Figure 3 assume termination with a 37.5- Ω resistor. When sync insertion is enabled, an additional current source is enabled providing a DC bias and head-room for negative sync insertion. A fixed RFS value of 3.8 kΩ (RFS(nom)) is suitable for most applications requiring 700-mV output levels. Copyright © 2008, Texas Instruments Incorporated Submit Documentation Feedback 5 Product Folder Link(s): THS8136 |
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