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AD8055 Datasheet(PDF) 12 Page - Analog Devices |
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AD8055 Datasheet(HTML) 12 Page - Analog Devices |
12 / 16 page AD8055/AD8056 Rev. J | Page 12 of 16 APPLICATIONS FOUR-LINE VIDEO DRIVER Between these points, a feedback resistor can be used to close the loop. As in the case of a conventional op amp inverting gain stage, an input resistor is added to vary the gain. The AD8055 is a useful low cost circuit for driving up to four video lines. For such an application, the amplifier is configured for a noninverting gain of 2, as shown in Figure 36. The input video source is terminated in 75 Ω and is applied to the high impedance noninverting input. /R The gain of this circuit from the input to AMP1 output is RF I, while the gain to the output of AMP2 is −R /R F I . The circuit therefore creates a balanced differential output signal from a single-ended input. The advantage of this circuit is that the gain can be changed by changing a single resistor, while still maintaining the balanced differential outputs. Each output cable is connected to the op amp output via a 75 Ω series back termination resistor for proper cable termination. The terminating resistors at the other ends of the lines divide the output signal by 2, which is compensated for by the gain of 2 of the op amp stage. 75Ω +5V –5V AD8056 402Ω 402Ω 402Ω 402Ω 49.9Ω 49.9Ω 1 2 3 8 AMP1 5 6 7 4 AMP2 0.1µF RF 402Ω RI 402Ω 10µF 0.1µF 10µF VIN +VOUT –VOUT For a single load, the differential gain error of this circuit was measured as 0.01%, with a differential phase error of 0.02°. The two load measurements were 0.02% and 0.03°, respectively. For four loads, the differential gain error is 0.02%, while the differential phase increases to 0.1°. VOUT3 AD8055 +5V –5V 6 7 2 3 4 75Ω 75Ω 75Ω 75Ω 75Ω 75Ω 75Ω 75Ω VOUT1 VOUT2 VOUT4 0.1µF 0.1µF 10µF 10µF 75Ω 402Ω 402Ω VIN Figure 37. Single-Ended-to-Differential Line Driver Figure 36. Four-Line Video Driver LOW NOISE, LOW POWER PREAMP SINGLE-ENDED-TO-DIFFERENTIAL LINE DRIVER The AD8055 makes a good, low cost, low noise, low power preamp. A gain-of-10 preamp can be made with a feedback resistor of 909 Ω and a gain resistor of 100 Ω, as shown in Creating differential signals from single-ended signals is required for driving balanced, twisted pair cables, differential input ADCs, and other applications that require differential signals. This can be accomplished by using an inverting and a noninverting amplifier stage to create the complementary signals. Figure 38. The circuit has a −3 dB bandwidth of 20 MHz. 0.1µF 10µF 0.1µF 10µF +5V –5V + AD8055 6 7 2 3 4 VOUT RS 909Ω 100Ω The circuit shown in Figure 37 shows how an AD8056 can be used to make a single-ended-to-differential converter that offers some advantages over the architecture previously mentioned. Each op amp is configured for unity gain by the feedback resistors from the outputs to the inverting inputs. In addition, each output drives the opposite op amp with a gain of −1 by means of the crossed resistors. The result of this is that the outputs are complementary and there is high gain in the overall configuration. Figure 38. Low Noise, Low Power Preamp with G = +10 and BW = 20 MHz With a low source resistance (< approximately 100 Ω), the major contributors to the input-referred noise of this circuit are the input voltage noise of the amplifier and the noise of the 100 Ω resistor. These are 6 nV/√Hz and 1.2 nV/√Hz, respectively. These values yield a total input referred noise of 6.1 nV/√Hz. Feedback techniques similar to a conventional op amp are used to control the gain of the circuit. From the noninverting input of AMP1 to the output of AMP2 is an inverting gain. |
Similar Part No. - AD8055_06 |
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Similar Description - AD8055_06 |
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