Help with op amp data sheet

Discussion in 'The Projects Forum' started by arenwi, Jun 10, 2015.

  1. arenwi

    Thread Starter Member

    Dec 29, 2014
    37
    0
    Hi every body.

    I was some days trying to make a linear amplifier for audio frecuencies (betwin 0 and 20000 Hz).
    I had started asembling and asembling circuits but coudnt find the solution.
    Now I need to start step by step to desing a good cyrcuit.

    I was having problems to find the caracteristic of lineality (betwin gain and frecuency) in mi op amp data shet´s, I think that I don´t intrepetate it in the right way.

    Im working with a simple inverter op amp sircuits with single supply, with op amps like:

    Linear Lt1078 http://www.linear.com/product/LT1078

    Texas TLV2264 http://www.ti.com/product/tlv2264


    Many thanks

    Aren
     
  2. MikeML

    AAC Fanatic!

    Oct 2, 2009
    5,450
    1,066
    To analyze the frequency response of any feedback amplifier system, we need to know the required voltage gain, minimum input impedance, minimum output load impedance, supply voltage, maximum amplitude of the the output, allowed noise figure, and distortion.

    The resistors, capacitors and opamp characteristics all follow from these specs.
     
  3. arenwi

    Thread Starter Member

    Dec 29, 2014
    37
    0
    Hi MIke,

    I would like to desing the circuit looking the specifications of the data sheet before.

    I think that if I dont use any filter on the circuit the values of the resistance are only used for the Gain but I nedd to know witch is the most gain with lineality betwin 0 and 20Khz before to desing it (I need this information of the data sheet) to know how many cascade op amps I need.

    I will work with 4.5 vots from a batery, needing 100x of gain and with a minimum imput impedance of 10k ohms.

    Using this circuit

    [​IMG]
    Also an inverter configuration will ve ok.
    BUt how could I obtain the frecuency response of mi circuit. Until I know I must to look inside of the data sheet of the op amp. But where??
     
  4. MikeML

    AAC Fanatic!

    Oct 2, 2009
    5,450
    1,066
    Here is a practical amplifier, showing bias and coupling capacitors. I show the Gain vs frequency at different values of R3 when the input is 40mVpp. Note that this is non-inverting configuration, where the gain is 1+R3/R4. Gains of 2, 5, 10 and 20 are shown.

    Note that the amplifier itself runs out of GainBandwidth product to be flat to 20kHz for gains => 10...

    75.gif
     
  5. AnalogKid

    Distinguished Member

    Aug 1, 2013
    4,540
    1,251
    One way to estimate if the opamp you have selected is good enough for the job is to look at the gain-bandwidth product on the datasheet. For example, what you need is a gain of 1oo (40 dB) and bandwidth of 20 kHz, for a GBW of 2 MHz. For the circuit to have a low output impedance, flat frequency response, and low distortion, you need at least 20 dB of negative feedback, for a total minimum forward gain of 60 dB. Looking at the open loop gain plot on the datasheet, see what the open loop gain is at 20 kHz. If it is less than 60 dB, your circuit will not have the performance you need.

    High performance audio is tough, and most general purpose opamps don't measure up. The LT1078 is an excellent part, but as shown above it is not going to work for you. Some opamps are specifically designed for audio applications, such as the NE5532/5534, Fairchild's RC series, Analog Devices SM series and many parts from TI (Burr Brown). THAT has a line of audio preamp chips with exceptional performance.

    ak
     
    arenwi likes this.
  6. arenwi

    Thread Starter Member

    Dec 29, 2014
    37
    0
    Really tahnks for your answers.

    Now I have some concepts mosre clear.

    Many thanks

    SOLVED
     
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