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ZL40123 Folha de dados(PDF) 2 Page - Zarlink Semiconductor Inc |
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ZL40123 Folha de dados(HTML) 2 Page - Zarlink Semiconductor Inc |
2 / 16 page ZL40123 Data Sheet 2 Zarlink Semiconductor Inc. Application Notes Current Feedback Op Amps Current feedback op amps offer several advantages over voltage feedback amplifiers: • AC bandwidth not dependent on closed loop gain • High Slew Rate • Fast settling time The architecture of the current feedback opamp consists of a high impedance non-inverting input and a low impedance inverting input which is always feedback connected. The error current is amplified by a transimpedance amplifier which can be considered to have gain where Zo is the DC gain. It can be shown that the closed loop non-inverting gain is given by where Av is the DC closed loop gain, Rf is the feedback resistor. The closed loop bandwidth is therefore given by and for low values of closed loop gain Av depends only on the feedback resistor Rf and not the closed loop gain. Increasing the value of Rf • Increases closed loop stability • Decreases loop gain • Decreases bandwidth • Reduces gain peaking • Reduces overshoot Using a resistor value of Rf=510Ω for Av=+2 V/V gives good stability and bandwidth. However since requirements for stability and bandwidth vary it may be worth experimentation to find the optimal Rf for a given application. Layout Considerations Correct high frequency operation requires a considered PCB layout as stray capacitances have a strong influence over high frequency operation for this device. The Zarlink evaluation board serves as a good example layout that should be copied. The following guidelines should be followed: • Include 6.8uF tantalum and 0.1uF ceramic capacitors on both positive and negative supplies • Remove the ground plane under and around the part, especially near the input and output pins to reduce parasitic capacitances • Minimize all trace lengths to reduce series inductance + = o o f f j Z f Z 1 ) ( + = o o f Z f fR j Av Vin Vout 1 f OL f o o CL R GB R Z f BW = = |
Nº de peça semelhante - ZL40123 |
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Descrição semelhante - ZL40123 |
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