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ADA4411-3 Fiches technique(PDF) 11 Page - Analog Devices |
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ADA4411-3 Fiches technique(HTML) 11 Page - Analog Devices |
11 / 16 page ADA4411-3 Rev. 0 | Page 11 of 16 APPLICATIONS OVERVIEW CUTOFF FREQUENCY SELECTION With its high impedance multiplexed inputs and high output drive, the ADA4411-3 is ideally suited to video reconstruction and antialias filtering applications. The high impedance inputs give designers flexibility with regard to how the input signals are terminated. Devices with DAC current source outputs that feed the ADA4411-3 can be loaded in whatever resistance provides the best performance, and devices with voltage outputs can be optimally terminated as well. The ADA4411-3 outputs can each drive up to two source-terminated 75 Ω loads and can therefore directly drive the outputs from set-top boxes, DVD players, and the like without the need for a separate output buffer. Four combinations of cutoff frequencies are provided for the video signals. The cutoff frequencies have been selected to correspond with the most commonly deployed component video scanning systems. Selection between the cutoff frequency combinations is controlled by the logic signals applied to the F_SEL_A and F_SEL_B inputs. Table 7 summarizes cutoff frequency selection. Table 7. Filter Cutoff Frequency Selection F_SEL_A F_SEL_B Y/G Cutoff Pb/B Cutoff Pr/R Cutoff 0 0 36 MHz 36 MHz 36 MHz Binary control inputs are provided to select cutoff frequency, throughput gain, and input signal. These inputs are compatible with 3 V and 5 V TTL and CMOS logic levels referenced to GND. The disable feature is asserted by pulling the DISABLE pin to the positive supply. The LEVEL1 and LEVEL2 inputs comprise a differential input that controls the dc level at the output pins. MULTIPLEXER SELECT INPUTS Selection between the two multiplexer inputs is controlled by the logic signals applied to the MUX inputs. Table 6 summarizes the multiplexer operation. THROUGHPUT GAIN The throughput gain of the ADA4411-3 signal paths can be either × 2 or × 4. Gain selection is controlled by the logic signal applied to the G_SEL pin. Table 6 summarizes how the gain is selected. DISABLE The ADA4411-3 includes a disable feature that can be used to save power when a particular device is not in use. As indicated in the Overview section, the disable feature is asserted by pulling the DISABLE pin to the positive supply. Table 6 summarizes the disable feature operation. The DISABLE pin also functions as a reference level for the logic inputs and therefore must be connected to ground when the device is not disabled. Table 6. Logic Pin Function Description DISABLE MUX G_SEL VS+ = Disabled 1 = Channel 1 Selected 1 = ×2 Gain GND = Enabled 0 = Channel 2 Selected 0 = ×4 Gain 0 1 36 MHz 18 MHz 18 MHz 1 0 18 MHz 18 MHz 18 MHz 1 1 9 MHz 9 MHz 9 MHz OUTPUT DC OFFSET CONTROL The LEVEL1 and LEVEL2 inputs work as a differential, input- referred output offset control. In other words, the output offset voltage of a given channel is equal to the difference in voltage between the LEVEL1 and LEVEL2 inputs, multiplied by the overall filter gain. This relationship is expressed in Equation 1. (1) ) )( ( ) ( G LEVEL LEVEL OUT VOS 2 1 − = LEVEL1 and LEVEL2 are the voltages applied to the respective inputs, and G is the throughput gain. For example, with the G_SEL input set for ×2 gain, setting LEVEL1 to 300 mV and LEVEL2 to 0 V shifts the offset voltages at the ADA4411-3 outputs to 600 mV. This particular setting can be used in most single-supply applications to keep the output swings safely above the negative supply rail. The maximum differential voltage that can be applied across the LEVEL1 and LEVEL2 inputs is ±500 mV. From a single-ended standpoint, the LEVEL1 and LEVEL2 inputs have the same range as the filter inputs. See the Specifications tables for the limits. The LEVEL1 and LEVEL2 inputs must each be bypassed to GND with a 0.1 μF ceramic capacitor. In single-supply applications, a positive output offset must be applied to keep the negative-most excursions of the output signals above the specified minimum output swing limit. |
Numéro de pièce similaire - ADA4411-3 |
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Description similaire - ADA4411-3 |
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