Negative swing with a DAC


Closed Thread
Results 1 to 8 of 8
  1. #1
    Join Date
    Jun 2007
    Location
    Mansfield, UK
    Posts
    697

    Default Negative swing with a DAC

    Hi, I have an 8-bit DAC which is currently outputting about 0-3V. After some filtering etc this goes into the line-in of an audio amplifier.

    Line level is supposed to swing from about -1.5 to 1.5V. I've seen online that this can be achieved by "biasing" the amplifier's ground to 1.5V.

    The issue I've got is that the amplifier is powered from the same power supply as the rest of the circuit. The reference ground on the amplifier is the same as the power ground so there's no way for me to bias it.

    Is there another way to get the required swing? I feel that I need to connect my DAC to -3V instead of ground but I don't have a negative supply.

  2. #2
    Join Date
    Sep 2009
    Posts
    737


    Did you find this post helpful? Yes | No

    Default Re: Negative swing with a DAC

    Just add high pass filter

  3. #3
    Join Date
    Jun 2007
    Location
    Mansfield, UK
    Posts
    697


    Did you find this post helpful? Yes | No

    Default Re: Negative swing with a DAC

    Sorry, I should mention that I only have 24V DC available from a switching PSU and the amplifier is single supply (not split).

    I could potentially move the entire amplifier ground up by 1.5V as 22.5V would still be enough to power it.
    A potential divider won't be suitable to hold the ground of a 100W amp though.

  4. #4
    Join Date
    Sep 2009
    Posts
    737


    Did you find this post helpful? Yes | No

    Default Re: Negative swing with a DAC

    Did you see my post?
    That is common way to remove dc offset and center signal around 0V.

  5. #5
    Join Date
    Mar 2003
    Location
    Commerce Michigan USA
    Posts
    1,166


    Did you find this post helpful? Yes | No

    Default Re: Negative swing with a DAC

    If it were me, I would vary the signal between 1 and 4 volts with the PIC, 2.5 volts being your artificial ground (bias) and then cap couple it to the amplifier. I have done this before with our radio repeater for the courtesy tone's.
    Dave Purola,
    N8NTA
    EN82fn

  6. #6
    Join Date
    Oct 2005
    Location
    Sweden
    Posts
    3,517


    Did you find this post helpful? Yes | No

    Default Re: Negative swing with a DAC

    I'm not sure why you're ignoring the idea of simply AC-coupling the signal into the amplifier but if that doesn't work for whatever reason it might be possible to use the PIC to generate a negative supply rail for the DAC using a chargepump circuit and the CCP module in PWM mode. It'll add circuitry though.

  7. #7
    Join Date
    Jun 2007
    Location
    Mansfield, UK
    Posts
    697


    Did you find this post helpful? Yes | No

    Default Re: Negative swing with a DAC

    pedja089:-
    I did see your post. Are you suggesting to use that circuit on the output from the DAC? I thought the sine wave was representing an AC supply.

    Dave/Henrik:-
    I've just done a bit of reading and it looks like "cap coupling", "AC-coupling" and pedja089's schematic are all the same thing. I will give that a go and see what happens.

    Henrik:-
    I have plenty of board space for once so if I do need to add extra stuff it won't be a problem.

  8. #8
    Join Date
    Sep 2009
    Posts
    737


    Did you find this post helpful? Yes | No

    Default Re: Negative swing with a DAC

    Yes, that circuit should be on output of DAC. And it is just first image from WEB.

Similar Threads

  1. Ti Dac 7553
    By GeoJoe in forum mel PIC BASIC Pro
    Replies: 5
    Last Post: - 28th August 2008, 21:29
  2. Looking for a DAC
    By RussMartin in forum Off Topic
    Replies: 4
    Last Post: - 25th November 2007, 07:21
  3. Using DAC's with pics
    By J_norrie in forum mel PIC BASIC Pro
    Replies: 3
    Last Post: - 27th March 2007, 15:00
  4. i2c with a dac
    By fabritio in forum mel PIC BASIC Pro
    Replies: 11
    Last Post: - 29th March 2006, 18:13
  5. dac
    By kaisersystems in forum mel PIC BASIC Pro
    Replies: 0
    Last Post: - 10th June 2005, 21:23

Members who have read this thread : 1

You do not have permission to view the list of names.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts