Bypass capacitors for Instrumentation amplifier

Discussion in 'The Projects Forum' started by working_on_EMG, Dec 29, 2010.

  1. working_on_EMG

    Thread Starter New Member

    Dec 4, 2010
    12
    0
    Hello everyone.

    I was reading the INA128 Texas Instruments instrumentation amplifier datasheet and came across this sentence:

    'Applications with noisy or high impedance power supplies may require decoupling capacitors as close as possible to the to the device pins as shown'

    I would like to ask what exactly are noisy and high impedance power supplies? Im powering this instrumentation amplifier with two 9V batteries to provide +/- 9V power supply, can two 9V batteries be considered as noisy or high impedance?
     
  2. edgetrigger

    Member

    Dec 19, 2010
    133
    19
    Your battery is neither high impedance nor noisy. Please connect it and amplify the signal you want to amplify.
     
    working_on_EMG likes this.
  3. edgetrigger

    Member

    Dec 19, 2010
    133
    19
    These bypass capacitors are dealt very well in one more thread in this forum, go through it for proper understanding of its need.
     
    working_on_EMG likes this.
  4. Ron H

    AAC Fanatic!

    Apr 14, 2005
    7,050
    657
    You should always use bypass capacitors for the power pins on amplifiers. They are like cheap insurance.
     
    working_on_EMG likes this.
  5. marshallf3

    Well-Known Member

    Jul 26, 2010
    2,358
    201
    Battery supply or not, ICs of any type have an inherent tendency to oscillate due to their high input impedances. 0.05 each from a local supplier or or a bag of them from Radio Shack and pick out some that are preferably 0.1 uF or better and put them as close to the Vcc and Vee pins to ground as you can.

    I've been through a lot of options and I tend to prefer keeping a few hundred of these around as they fit nicely on a circuit board or can be tacked onto the back directly to the pins if necessary:
    http://www.mouser.com/Search/Produc...5TAvirtualkey64600000virtualkey80-C410C104K5R
    http://www.kemet.com/kemet/web/home...files/F3101_Aximax.pdf/$file/F3101_Aximax.pdf

    The picture is far from representative but the dimensions are, they're tiny little things are even far smaller than a standard 1/4W 1% resistor. I've used quite a few different types over the years but it looks like I can get a price of 0.02 if I order 750 the next time so I will likely be including them as opposed to others in my designs from here on out. PCB real estate can become a real issue when you try to maximize density for the smallest project box available, it also comes into play when designing and paying for the boards to be made.

    If you intend to get into experimentation on any sort of basis I'd grab a few of of these to have around as they're far from new and I've never had one fail, name brand stuff. I went ahead and wrote Mouser to update their picture and they're pretty good at handling my little requests when I see something that isn't correct.
     
    working_on_EMG likes this.
  6. working_on_EMG

    Thread Starter New Member

    Dec 4, 2010
    12
    0
    Thanks to all for the sharing this information. In the INA128 instrumentation amplifier data sheet they mentioned about 0.1 microfarad bypass capacitors however they did not mention the type of capacitors suitable to be used as bypass capacitors. I have many 0.1 microfarad ceramic capacitors, will these ceramic capacitors work equally well as multilayer ceramic capacitors for bypassing?

    In another datasheet for an operational amplifier OPA2604, they specifically mentioned using 1 microfarad tantalum capacitors as bypass capacitors. If I were to use 0.1 microfarad ceramic capacitors, can these capacitors 'bypass' properly?
     
    Last edited: Dec 29, 2010
Loading...