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AD8145 Datasheet(PDF) 15 Page - Analog Devices |
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AD8145 Datasheet(HTML) 15 Page - Analog Devices |
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15 / 24 page  AD8145 Rev. A | Page 15 of 24 APPLICATIONS INFORMATION OVERVIEW The AD8145 contains three independent active feedback amplifiers that can be effectively applied as differential line receivers for red-green-blue (RGB) signals or component video signals, such as YPbPr, transmitted over UTP cable. The AD8145 also contains two general-purpose comparators with hysteresis that can be used to receive digital signals or to extract video synchronization pulses from received common-mode signals that contain encoded synchronization signals. The comparators, which receive power from the positive supply, are referenced to GND and require greater than 4.5 V on the positive supply for proper operation. If the comparators are not used, then a split ±2.5 V can be used with the amplifiers operating normally. The AD8145 includes a power-down feature that can be asserted to reduce the supply current when a particular device is not in use. BASIC CLOSED-LOOP GAIN CONFIGURATIONS Each amplifier in the AD8145 comprises two transconductance amplifiers—one for the input signal and one for negative feedback. Note that the closed-loop gain of the amplifier used in the signal path is defined as the single-ended output voltage of the amplifier divided by its differential input voltage. Therefore, each amplifier in the AD8145 provides differential-to-single-ended gain. Additionally, the amplifier used for feedback has two high impedance inputs—the feedback input, where the negative feedback is applied, and the REF input, that can be used as an independent single-ended input to apply a dc offset to the output signal. The AD8145 contains on-chip feedback networks between each amplifier output and its respective feedback input. The closed- loop gain of the amplifier is set to 1 by connecting the amplifier output directly to its respective GAIN_x pin. Doing this places the on-chip resistors and capacitor in parallel across the amplifier output and feedback pin. The small feedback capacitor mitigates the effects of the summing-node capacitance, which is most problematic in the unity gain case. Closed-loop gain of an amplifier is set to 2 by connecting the respective GAIN_x pin to a reference voltage, often directly to ground. In Figure 1, R = 350 Ω and C = 2 pF. Some basic gain configurations implemented with an AD8145 amplifier are shown in Figure 33 through Figure 36. GAIN REF R R 0.01µF 0.01µF +5V –5V C OUT VOUT VIN VREF Figure 33. Basic Gain = 1 Circuit: VOUT = VIN + VREF The gain equation for the circuit in Figure 33 is VOUT = VIN + VREF (1) In this configuration, the voltage applied to the REF pin appears at the output with a gain of 1. Figure 34 illustrates one way to operate an AD8145 amplifier with a gain of 2. GAIN REF R R 0.01µF 0.01µF +5V –5V C VREF VOUT VIN Figure 34. Basic Gain = 2 Circuit: VOUT = 2(VIN + VREF) The gain equation for the circuit in Figure 34 is VOUT = 2(VIN + VREF) (2) |
Similar Part No. - AD8145_15 |
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Similar Description - AD8145_15 |
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