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Confirmation of AD8055 Output Voltage Swing Specification

Thread Summary

The user inquired about the maximum output voltage swing of the AD8055 under ±5V supply conditions. The final answer clarified that the datasheet specifies a minimum output swing of ±2.9V and a typical swing of ±3.1V for RL = 150 ohms, with no guaranteed maximum. For output limiting, a small series resistor and low-capacitance Schottky diodes are recommended to minimize impact on signal integrity and bandwidth.
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Category: Hardware

Dear ADI team.

I would like to inquire about the output voltage range of the AD8055.

According to the datasheet, the output voltage swing is specified as approximately ±3.9 V to ±4.1 V (typical), depending on the load condition, when operating with a ±5 V supply.

Could you please let us know whether there is a specified maximum output voltage swing value (for example, a guaranteed maximum or limit specification) under these conditions?

My customer are currently evaluating the protection design for a subsequent stage circuit. If they can accurately determine the upper limit of the AD8055 output voltage, it may be possible to eliminate the output protection circuitry intended to limit the voltage.

Additionally, if the maximum output voltage is not specified, could you please advise on a suitable method or circuit for clamping the output voltage of a high-speed signal line?

We would appreciate any recommendations for minimizing the impact on signal integrity and bandwidth while providing output voltage limiting.

Best regards,

Yoshiba

  • Hi  

    Just to clarify, with ±5V supplies, the AD8055 datasheet specifies an output voltage swing of ±2.9V minimum and ±3.1V typical for RL = 150 ohms. Figure 30 also shows the typical output swing versus load temperature. I could not find the ±3.9V to ±4.1V values given.

    There is no guaranteed maximum output voltage or saturation limit specified, so the output swing specification cannot be used as an absolute upper limit for the voltage that may appear at the output.

    For output limiting, a common approach for a high-speed signal path is to use a small series resistor followed by low-capacitance Schottky clamp diodes connected to the appropriate clamp rails. The series resistor limits the clamp current and also helps isolate the diode capacitance from the AD8055 output.

    To minimize the effect on bandwidth and signal integrity, the diode capacitance and series resistance should be kept as low as practical, with short PCB traces. The datasheet also recommends a small series output resistor when driving capacitive loads to reduce peaking and maintain stability. Figure 41 shows approximately 25 ohms for larger capacitive loads under the specific test conditions used there.

    Best Regards,
    Ian

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