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OPA861 Datasheet(PDF) 20 Page - Texas Instruments |
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OPA861 Datasheet(HTML) 20 Page - Texas Instruments |
20 / 32 page 6 3 0 −3 −6 −9 Frequency (Hz) 1M 10M 100M 1G 5.6dB 600 Ω 600 Ω V IN1 V CM V IN2 R E 600 Ω ADS5272 OPA861 OPA861 3 0 -3 -6 -9 -12 -15 -18 -21 -24 -27 -30 -33 -36 -39 -42 -45 -48 Frequency(Hz) 10k 100k 1M 10M 100M 1G 50MHzFilter 20MHzFilter 1MHzFilter ForAllFilters: R =R = 2 ¥ 3 R =R =R 1 1S 2S 3S =1/2R =R R =R =R 1M 2M 0 C =C =C 1 2 0 OPA861 SBOS338G – AUGUST 2005 – REVISED MAY 2013 www.ti.com A few designs for a low-pass filter are shown in High-CMRR, Moderate Precision, Differential Figure 47 and Table 2. I/O ADC Driver The circuit shown in Figure 48 depicts an ADC driver Table 2. Component Values for Filters Shown In implemented with two OPA861s. Since the gain is set Figure 47 here by the ratio of the internal 600 Ω resistors and fO R RO CO RE, its accuracy will only be as good as the input 1MHz 150 100 2nF resistor of the ADS5272. The small-signal frequency response for this circuit has 150MHz at –3dB 20MHz 150 100 112.5pF bandwidth for a gain of approximately 5.6dB, as 50MHz 150 100 25pF shown in Figure 49. The advantage of this circuit lies in its high CMRR to 100kHz; see Figure 50. This circuit also has more than 10 bits of linearity. Figure 47. Butterworth Low-Pass Filter with the Universal Active Filter Figure 48. High CMRR, Moderate Precision, Differential I/O ADC Driver The advantages of building active filters using a Current Conveyor structure are: • The increase in output resistance of operational amplifiers at high frequencies makes it difficult to construct feedback filter structures (decrease in stop-band attenuation). • All filter coefficients are represented by resistances, making it possible to adjust the filter frequency response without affecting the filter coefficients. • The capacitors which determine the frequency are located between the ground and the current source outputs and are thus grounded on one side. Therefore, all parasitic capacitances can be viewed as part of these capacitors, making them easier to comprehend. • The features which determine the frequency Figure 49. ADC Driver, Small-Signal Frequency characteristics are currents, which charge the Response integration capacitors. This situation is similar to the transfer characteristic of the Diamond Transistor. 20 Submit Documentation Feedback Copyright © 2005–2013, Texas Instruments Incorporated Product Folder Links: OPA861 |
Similar Part No. - OPA861_15 |
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Similar Description - OPA861_15 |
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