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ADV101 Datasheet(PDF) 8 Page - Analog Devices |
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ADV101 Datasheet(HTML) 8 Page - Analog Devices |
8 / 12 page ![]() ADV101 –8– REV. B A resistance RSET connected between FS ADJUST and GND determines the amplitude of the output video level according to the following equations: IOG (mA) = 12,082 × V REF (V)/RSET (Ω) (1) IOR, IOB (mA) = 8,628 × V REF (V)/RSET (Ω) (2) If SYNC is not being encoded onto the green channel, then Equation 1 will be similar to Equation 2. Using a variable value of RSET, as shown in Figure 4, allows for accurate adjustment of the analog output video levels. Use of a fixed 560 Ω R SET resistor yields the analog output levels as quoted in the specification page. These values also correspond to the RS-343A video waveform values as shown in Figure 3. TO DACs ADV101* V AA V REF GND 1k Ω FS ADJUST SET R 560 Ω 500 Ω 100 Ω *ADDITIONAL CIRCUITRY, INCLUDING DECOUPLING COMPONENTS, EXCLUDED FOR CLARITY ANALOG POWER PLANE COMP 0.1 µF 5V + AD589 (1.235V VOLTAGE REFERENCE) 4mA I REF ~ ~ Figure 4. Reference Circuit D/A Converters The ADV101 contains three matched 8-bit D/A converters. The DACs are designed using an advanced, high speed, segmented architecture. The bit currents corresponding to each digital in- put are routed to either the analog output (bit = “1”) or GND (bit = “0”) by a sophisticated decoding scheme. As all this cir- cuitry is on one monolithic device, matching between the three DACs is optimized. As well as matching, the use of identical current sources in a monolithic design guarantees monotonicity and low glitch. The onboard operational amplifier stabilizes the full-scale output current against temperature and power supply variations. Analog Outputs The ADV101 has three analog outputs, corresponding to the red, green and blue video signals. A fourth analog output (ISYNC) can be used if it is required to encode video synchroni- zation information onto the green signal. In this case, ISYNC is connected to IOG. (See “Video Synchronization and Control” section.) The red, green and blue analog outputs of the ADV101 are high impedance current sources. Each one of these three RGB cur- rent outputs is capable of directly driving a 37.5 Ω load, such as a doubly terminated 75 Ω coaxial cable. Figure 5a shows the DACs IOR, IOG, IOB Z = 75 Ω O (CABLE) Z = 75 Ω S (SOURCE TERMINATION) Z = 75 Ω L (MONITOR) TERMINATION REPEATED THREE TIMES FOR RED, GREEN AND BLUE DACs Figure 5a. Analog Output Termination for RS-343A DACs IOR, IOG, IOB Z = 75 Ω O (CABLE) Z = 150 Ω S (SOURCE TERMINATION) Z = 75 Ω L (MONITOR) TERMINATION REPEATED THREE TIMES FOR RED, GREEN AND BLUE DACs Figure 5b. Analog Output Termination for RS-170 required configuration for each of the three RGB outputs con- nected into a doubly terminated 75 Ω load. This arrangement will develop RS-343A video output voltage levels across a 75 Ω monitor. A suggested method of driving RS-170 video levels into a 75 Ω monitor is shown in Figure 5b. The output current levels of the DACs remain unchanged, but the source termination resistance, ZS, on each of the three DACs is increased from 75 Ω to 150 Ω. More detailed information regarding load terminations for vari- ous output configurations, including RS-343A and RS-170, is available in an application note entitled “Video Formats & Required Load Terminations” available from Analog Devices, publication number E1228-15-1/89. Figure 3 shows the video waveforms associated with the three RGB outputs driving the doubly terminated 75 Ω load of Figure 5a. As well as the gray scale levels, black level to white level, the diagram also shows the contributions of SYNC and BLANK. These control inputs add appropriately weighted currents to the analog outputs, producing the specific output level requirements for video applications. Table I details how the SYNC and BLANK inputs modify the output levels. Gray Scale Operation The ADV101 can be used for stand-alone, gray scale (mono- chrome) or composite video applications (i.e., only one channel used for video information). Any one of the three channels, red, green or blue can be used to input the digital video data. The two unused video data channels should be tied to logical zero. OBSOLETE |
Similar Part No. - ADV101_15 |
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