Programable analog delay line

Discussion in 'General Electronics Chat' started by jean_jean, Apr 2, 2016.

  1. jean_jean

    Thread Starter New Member

    Apr 2, 2016
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    Dear all,

    I have a project where I need to delay a signal with about tens of microseconds (max. 50µs) and I can only find digital delay lines or 64µs delay lines for PAL TV systems.

    The signal I am working with has a max amplitude of 1Vpp, with a 1.5MHz max frequency.

    Can anybody help me?

    Best regards,
    Jean
     
  2. k7elp60

    Senior Member

    Nov 4, 2008
    478
    69
    The first thing I thought of was a piece of coaxial cable, but then I did some research and found coax may have a delay of 1.5ns per foot.
    Then I thought of a low pass filter. At 1.5Mhz with a phase shift of 60 degrees that would be about .11us and you would have less than 1V pp out. So I have no suggestion for you. Just sharing my thoughts.
     
  3. MrAl

    Well-Known Member

    Jun 17, 2014
    2,440
    492
    Hello,

    You might have to specify what this will be used for exactly.

    First thought, CMOS bucket brigade analog delay chip.
    Second thought, microcontroller with an ADC and a DAC, simple DSP algorithm.
     
  4. GopherT

    AAC Fanatic!

    Nov 23, 2012
    6,067
    3,837

    You could try the PT2399 chip. It is an audio echo chip but can delay most any signal.

    They are no longer made but old stock is available on eBay and some other distributors.
     
  5. DickCappels

    Moderator

    Aug 21, 2008
    2,662
    633
    You can buy or make passive LC delay lines. This application note explains how they work and you can actually design your own lumped LC delay line from the information provided.

    The application note is at the link below.
    http://www.rhombus-ind.com/dlcat/app1_pas.pdf
     
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  6. crutschow

    Expert

    Mar 14, 2008
    13,052
    3,244
    What is the bandwidth of the signal you want to delay?
    Does the delay have to be constant over that bandwidth?
     
  7. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    Excellent link from DC.

    In 11 days, April 14th marks the 60th anniversary of the introduction of broadcast quality video recording and playback. Due to the mechanical nature of the record/playback transport and rotating heads, there is considerable timebase error in a recovered video signal. To correct this, Ampex developed the AMTEC (AMpex Time Element Corrector) device, a voltage-variable L-C video delay line based on the concepts in Dick's PDF, with varactor diodes for the capacitors. This reduced the timebase error down to 1 us p-p. A second device, the ColorTEC, used the same approach to get the color phase error down to nanoseconds. In the late 60's Ampex introduced the AVR-1. It replaced the voltage-variable line with a group of fixed delay lines in binary increments (1 us, 2us, 4us, 8us, etc.) with high-quality analog switches to insert them in the signal path as needed. Maintenance manuals for the VR-1200, VR-2000, AVR-1, AMTEC, and ColorTEC are wandering around the innergoogle, complete with schematics. Or a local TV station might have them buried in a back room.

    Added: many long-time delay devices are acoustic glass lines. Anderson made them back when, don't know who does now (and kinda surprised they're still around).

    ak
     
    Last edited: Apr 3, 2016
    RichardO likes this.
  8. RichardO

    Well-Known Member

    May 4, 2013
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    Up until that time recording of TV broadcasts was done on film. :eek: The recording was done to allow live TV broadcoasts from the east coast to be delayed for playing at a more suitable time farther west in the US. The film was usually recycled. In rare cases, film has been found holding long-ago TV programs that would otherwise be forever lost to time.
     
  9. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    Not sure what you mean by recycled, as the film was one-use only. Kinescope recordings were used for most national program distribution until a nationwide electronic signal path was completed in 1951. After that, kines were used for time zone delays. When videotape took over in the late 50's, kines were used for simultaneous backup recordings because VT wasn't trusted. and rightly so - those early machines were cranky.

    ak
     
  10. RichardO

    Well-Known Member

    May 4, 2013
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    By "recycled", I meant recovering the silver.

    Thanks for the more detailed history. :D
     
  11. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    Having built both, I recommend the switched fixed lines over a single voltage-variable line. The impedance, bandwidth and transient performance are much easier to control. There are transients at the switch points, although today's mux chips are almost glitch-free. It wasn't a problem with video because we did the switching during horizontal blanking. What is the signal you are delaying?

    ak
     
  12. jean_jean

    Thread Starter New Member

    Apr 2, 2016
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    The bandwidth is around 400kHz, with a central frequency of 1MHz. THe delay has to be constant over the bandwidth.
     
  13. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    Min and max delay times?
    Min and max voltage peaks?
    Places in the signal to hide small glitches?
    Signal characteristics (modulated sinewave, digital media stream, etc.)?

    ak
     
  14. jean_jean

    Thread Starter New Member

    Apr 2, 2016
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    Hi,

    The signal I am trying to delay is a modulated sine wave, 1Vpp and yes, the signal has places where glitches can be hid.
     
  15. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    Max and min delay times?
    Delay time resolution - minimum delay time increment?

    ak
     
  16. jean_jean

    Thread Starter New Member

    Apr 2, 2016
    7
    0
    A minimum of 10µs, maximum 50µs, increment of 5µs.
     
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