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THP210: Static operating point

zhang ping
Genius 3865 points

Part Number: THP210

1. Does the input in + and in - of thp210 chip provide internal static working point?

2. Please recommend the bandpass filter parameters of this chip. The requirement is 300Hz ~ 1500hz, and the gain is about 40dB.

  • 0
    Guru 140200 points

    Hi Zhang,

    why not running the

    THP210 TINA-TI Reference Design

    What bandpass filter are thinking about? There are zillions of possible bandpass filters all fullfilling 300Hz...1500Hz and 40dB gain Relaxed

    Kai

  • 0 in reply to kai klaas69
    TI__Guru 55466 points

    Hello Zhang,

    The THP210 is a fully-differential amplifier (FDA).  The VOCM pin voltage sets the common-mode voltage of the output differential signal, where the VOCM pin is in many cases biased around mid-supply.  On a fully-differential amplifier, the output stage (OUT+ and OUT-) provides a fully-differential symmetrical signal around the VOCM voltage.

    The voltage right at the (IN+) and (IN-) FDA pin terminals is not fixed and is a function of the input signal applied at the input resistors and the FDA output voltage.  Essentially, a voltage divider forms between the RF feedback and the RG input resistors of the FDA.

    For example, in the below figure, the FDA is set with a gain of 2 V/V, and VOCM=+2.5V.

    Applying a differential input signal of +1V with 2.5V common-mode, produces a differential output signal of +2V with a common-mode of +2.5V as expected; where the output at the FDA output is OUTP = +3.5V and OUTN=+1.5V; and the voltage at the input resistors is RG2(+) = +3V and RG1(-) =+2V

    The resulting voltage at the IN(-) terminal is +2.5V as shown below.  Essentially the voltage at the IN(-) terminal is the superposition of the RG1 input voltage divided by the ratio RF1/(RF1+RG1) and the OUTP voltage divided by the ratio RG1/(RG1+RF1).  As long as the FDA is inside its linear region, the voltage on the IN(-) and IN(+) terminals is approximately the same (small offset between the input terminals of ~10µV typical). An example using the TINA simulation is below.

     

     

    If you would like to learn more about fully-differential amplifiers, please review the TI precision lab series on fully differential amplifiers.

    TI Precision Labs- Fully Differential Amplifiers

    As Kai has mentioned, there are many possible bandpass filter possibilities depending on the application requirements that may fulfill the ~500 to ~1500Hz, Gain=100V/V=40dB bandpass requirement; and you will need to decide on the number of stages / filter order and required frequency response characteristic (Chebyshev, Butterworth, etc) according to the application requirements prior designing the circuit. 

    Thank you and Regards,

    Luis