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OPA861 Fiches technique(PDF) 12 Page - Texas Instruments |
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OPA861 Fiches technique(HTML) 12 Page - Texas Instruments |
12 / 28 page www.ti.com APPLICATION INFORMATION TRANSCONDUCTANCE (OTA) SECTION—AN BASIC CONNECTIONS 1 3 2 C E B C E B V IN1 I OUT V IN2 V IN1 I OUT V IN2 CCII+ Z Macro Transistor Current Conveyor II+ Voltage−Controlled Current Source Transconductor (used here) Diamond Transistor 1 2 3 4 8 7 6 5 R S (25 Ωto 200Ω) R C 0.1 µF R ADJ 250 Ω −5V(1) V IN + 2.2 µF 0.1 µF Solid Tantalum +5V(1) + 2.2 µF Solid Tantalum R Q = 250Ω, roughly sets IQ = 5.4mA. NOTE: (1) V S = ±6.5V absolute maximum. +V S −V S OPA861 SBOS338 – AUGUST 2005 The OPA861 is a versatile monolithic transconductance amplifier designed for OVERVIEW wide-bandwidth systems, including high-performance video, RF, and IF circuitry. The operation of the The symbol for the OTA section is similar to a OPA861 is discussed in the OTA (Operational transistor (see Figure 26). Applications circuits for the Transconductance Amplifier) section of this data OTA look and operate much like transistor cir- sheet. Over the years and depending on the writer, cuits—the transistor is also a voltage-controlled cur- the OTA section of an op amp has been referred to rent source. Not only does this characteristic simplify as a Diamond Transistor, Voltage-Controlled Current the understanding of application circuits, it aids the source, Transconductor, Macro Transistor, or positive circuit optimization process as well. Many of the second-generation current conveyor (CCII+). Corre- same intuitive techniques used with transistor designs sponding symbols for these terms are shown in apply to OTA circuits. The three terminals of the OTA Figure 26. are labeled B, E, and C. This labeling calls attention to its similarity to a transistor, yet draws distinction for clarity. While the OTA is similar to a transistor, one essential difference is the sense of the C-output current: it flows out the C terminal for positive B-to-E input voltage and in the C terminal for negative B-to-E input voltage. The OTA offers many advantages over a discrete transistor. The OTA is self-biased, simplify- ing the design process and reducing component count. In addition, the OTA is far more linear than a transistor. Transconductance of the OTA is constant over a wide range of collector currents—this feature implies a fundamental improvement of linearity. Figure 27 shows basic connections required for operation. These connections are not shown in sub- sequent circuit diagrams. Power-supply bypass ca- pacitors should be located as close as possible to the Figure 26. Symbols and Terms device pins. Solid tantalum capacitors are generally best. Regardless of its depiction, the OTA section has a high-input impedance (B-input), a low-input/output impedance (E-input), and a high-impedance current source output (C-output). Figure 27. Basic Connections 12 |
Numéro de pièce similaire - OPA861 |
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Description similaire - OPA861 |
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