ZL40122

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

It can be shown that the closed loop non-inverting gain is given by

• Increases closed loop stability

• Decreases loop gain

• Decreases bandwidth

• Reduces gain peaking

• Reduces overshoot

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

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