This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

LOG200: Alternatives to AD538

Part Number: LOG200
Other Parts Discussed in Thread: LOG114

Tool/software:

Hi,

AD538: https://www.analog.com/media/en/technical-documentation/data-sheets/AD538.pdf

As an alternative to AD538, we are considering a configuration with a LOG amplifier and an op-amp that performs exponential conversion. As for the LOG amplifier, we found LOG200, but it has not been released yet. Therefore, could you tell us a released LOG amplifier that has similar specifications to AD538?

Also, could you introduce an op-amp that performs exponential conversion that can be used as an alternative?

Best Regards,

Nishie

  • HI Nishie,

    The LOG200 is a current-to-voltage conversion amplifier. The LOG200 features two logarithmic amplifiers followed by a high-accuracy differential amplifier that convert current signals into a voltage representing the log compressed ratio of the two currents. The device is scheduled for release this fourth quarter of 2024. The device uses input currents I1 and I2.  I2 is typically connected to a reference current of 1uA.

    See LOG200 block diagram and transfer function below, where K = 250mV/decade.

    The device you show above performs an exponential /multiplication and divisions of voltages in the form of:

    Vo = Vy (Vz / Vx ) m

    Hence, the LOG200 current input, voltage output logarithmic conversion amplifier is not a similar function.

    From the Logarithmic amplifier family, the LOG200 used with series input resistors could be used to perform the logarithmic output function of the operation.  The LOG114 is the previously released device performing with a similar function of the LOG200.  However, we do not offer the antilog block in an integrated circuit.

    Hence, unfortunately, we do not offer a device that offers this function in an integrated device in the portfolio.

    Thank you and Regards,

    Luis

  • Hi Luis-san,

    Thank you for your support.

    I understood that it is difficult to realize the functions of AD358 with LOG200 and LOG114. If you have any application notes or reference designs for implementing exponential arithmetic circuits using other operational amplifiers, please share them with me

    Best Regards,

    Nishie.

  • HI Nishie,

    The Application Note, AN-30 Log Converters features a discrete anti-log generator example using discrete transistors/op-amps on Figure 3, page 5; also mentioned/explained briefly on page 3.

    https://www.ti.com/lit/an/snoa641b/snoa641b.pdf

    Thank you and Best Regards,

    Luis