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logarithmic amplification

user6360432
Intellectual 320 points

Amplification pulse signal, pulse width 3ns, frequency 100MHz, pulse rise time 1.7ns, which logarithmic amplifiers chip can be recommended? Must the rising time of the amplifier I choose less than 3 ns？

  • 0
    Guru 140200 points

    Many more details are necessary to answer your questions :-)

    Kai

  • 0
    TI__Genius 10850 points

    Hi User,

    Here is a table of all of our logarithmic amplifiers: https://www.ti.com/amplifier-circuit/special-function/logarithmic/products.html

    Our LOG amp expert is on Holiday, so please accept our delayed replies. 

  • 0 in reply to kai klaas69
    Intellectual 320 points

    I want to use a logarithmic amplifier for Gaussian pulse with full pulse width of 3.4ns and half pulse width of 1.7ns, the output pulse width is required to be constant and undistorted. When I choose an amplifier, should I choose a device with response time less than 1.7ns? Is 10% - 90% rising time in the manual an indicator that I should care about? Or should I pay attention to the index of the slew rate?

  • 0 in reply to user6360432
    Guru 140200 points

    Below you see a simple log amp.

    user_logamp.TSC

    Here's the transient response of a sine with different offsets:

    Is this what you expected to see?

    Kai

  • 0
    TI__Guru* 93105 points

    Hi,

    TI does not produce any log amplifier products for frequencies usable above about 5 MHz. Kai's simple log amplifier might is plausible but might be difficult to realize at a frequency such as 100 MHz. The junction capacitance of the diode used as the logging element and other circuit capacitances become frequency limiting factors.

    If you can't find some 100+ MHz log amplifiers produced by some other company, you might try applying Kai's circuit by using very high speed operational amplifiers, and a diode having extremely low junction capacitance. Then see what you get in terms of performance at 100 MHz.

    Regards, Thomas

    Precision Amplifiers Applications Engineering

  • 0 in reply to Thomas Kuehl
    Guru 140200 points

    Hi Thomas,

    I didn't want to offer a suited log amplifier but only wanted to give a response to the following user's statement:

    I want to use a logarithmic amplifier for Gaussian pulse with full pulse width of 3.4ns and half pulse width of 1.7ns, the output pulse width is required to be constant and undistorted.

    I wanted to demonstrate that the Gaussian pulse will no longer have the same FWHM after taking the logarithm and that the degree of distortion considerably depends on the offset voltage the Gaussian pulse is sitting on.

    Kai

  • 0 in reply to kai klaas69
    TI__Guru* 93105 points

    Hi Kai,

    I understand. Thank you for your response and input. Hopefully the information was helpful to him.

    Regards, Thomas

    Precision Amplifiers Applications Engineering