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Have a question about ADCs or DACs? Ask our Expert, Nick Gray

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Nick Gray

 

Nicholas Gray

Nicholas has worked in the Semiconductor industry for over 30 years and has authored a number of published articles about data converters (ADCs and DACs) and signal integrity issues.

 

  • 1. Re: Have a question about ADCs or DACs? Ask our Expert, Nick Gray
    Biswajit Level 1

    Dear Sir,

     

    I will be highly greatful to you if you can provide any ingormation on 7 segment 4 digit 28 pins LCD Decoder driver. I am in great need of this. If possible can you suggest some 7 segment LED decoder driver also. It would be nice of you if you can help me in this.

     

    With Regards

    Biswajit Acharjee

  • 2. Re: Have a question about ADCs or DACs? Ask our Expert, Nick Gray
    nickgray e14 Expert

    Good Day,

     

    I am sorry that I did not see this question from a month ago and LCD drivers are not exactly my strong point, but I will do my best to help. I can certainly recommend some products, but I do not know just what kind of information you need besides that.

     

    If your LCD is miltiplexed, you can use any of these decoder/drivers:

    HCF4543B from SGS Thompson Microelectronics

    CD4511B from Texas Instruments

    MAX7231, MAX7232, MAX7233 and MAX7234 from Maxim Integrated Products

     

    If your display is not multiplexed but has separate pins for each segment, finding a driver for it is more difficult. The only device that I am aware of that will easily do the job is the PT6530 from Princeton Technology in Taiwan, although this device has more capability than you really need and comes in a rather large package. But, with a little ingenuity you can probably get the above multiplexed devices to do the job.

     

    If you tell me a little more about just what information you need and the part type of the display you are using, I might be able to offer more help. At least, I hope so.

     

    - Nick Gray

  • 3. Re: Have a question about ADCs or DACs? Ask our Expert, Nick Gray
    f.rochais@comex.fr Level 1

    Good mornin Sir,

     

    I don't if i have to post here, and if i have to post to you. If not, please forward my demand.

    I'm in design step about a video switch .. I need to switch 4 video input (not HD) to a single ouput.. (The goal is to use only one coaxial line for 4 caméras.)

    A MCU will control this chip with selection bit (easier than serial communiations I²C..)

    I don't need low power consumption. I have to care noise signals because the other part of this board will switch power relays so the design of layout will be fastidious.

    I'm looking for chips which do this and the most simple and smaller.

    I've found Intersil # HA4314BCBZHA4314BCBZ.. but i would ask you if you know other chips, other way, any ideas to do this.

    Thank you.

     

    Best regards,

    Florent ROCHAIS

  • 4. Re: Have a question about ADCs or DACs? Ask our Expert, Nick Gray
    nickgray e14 Expert
    Hello, Florent –

    What you are looking for is called a Video Crosspoint Switch. The configuration you want is a 4 X 1 (4 input, one output). It is possible to use a larger array (4 X 4,  8 X 4,  8 X 8, etc), but large arrays must come in larger packages and generally cost more. While better performance can usually be achieved with surface mount packages compared with through-hole packages such as DIP, this is not always true and will depend somewhat upon your board layout and component placement.

    While I am sure there are more, the video crosspoint switches I am aware of include the following:
    HA4344B from Intersil – 4 X 1, 350 MHz Bandwidth, 16-pin SOIC package
    HA4404B from Intersil – 4 X 1, 330 MHz Bandwidth, 16-pin SOIC package
    ISL59444 from Intersil – 4 X 1, 1000 MHz Bandwidth, 16-pin SOIC package
    MAX456 from Maxim – 8 X 8, 35 MHz Bandwidth, 40-pin DIP and 44-pin PLCC packages
    ADV3221 from Analog Devices – 4 X 1, 650 MHz Bandwidth, 16-pin SOIC package, Gain = 1
    ADV3222 from Analog Devices – 4 X 1, 650 MHz Bandwidth, 16-pin SOIC package, Gain = 2

    - Nick Gray
  • 5. Re: Have a question about ADCs or DACs? Ask our Expert, Nick Gray
    f.rochais@comex.fr Level 1

    Thank you.

    I'll test 4x1 models before PCB routing.

    Would you have advices for routing of video signals ? I did not have any lesson about that at school and no colleague haf already made a PCB with videos signals. If you know a website where this is explained or maybe a lesson ...

    Anyway thank you for your help.

    Best regards,

    FLorent

  • 6. Re: Have a question about ADCs or DACs? Ask our Expert, Nick Gray
    nickgray e14 Expert

    Some time ago (more than 10 years ago, I wrote a technical article on this and have been unsuccessfully trying to find it. The basic idea is to use RF layout rules. Essentially, this means keeping high level signals well away from lower level signals, keeping the signal path in one board layer as much as possible, treat interconnects as transmission lines (not like simple traces), maintain a constant impedance along any all signal lines, always have a ground layer in adjacent to any signal layer (no traces in the ground layer). IF you know how to do it, you can modify some of these rules, but you absolutely must know what you are doing. There is much more that I could say, but I do not know just how to word it at this time. I will try to consider how to say it and put it into my blog.

     

    Good luck!

  • 8. Re: Have a question about ADCs or DACs? Ask our Expert, Nick Gray
    Al@Mond Level 2

    Nick:  I'm an ancient engineer with a modern-day need for an improved hearing aid.  What I need and what I want to develop is a simpler yet more effective digital hearing aid. All hearing aids leave one  with the  ' I hear but I don't understand'  feeling which is common-place to most hard of hearing (HOH) individuals..  In order to improve on these hearing aids, I want to copy the  design of a digital audio amplifier and add on one more stage.  That stage would take the output voltages from the A to D converter and modify it to a new set of voltages which are more compatible with the HOH  ear.  It has been suggested that I create a look-up table to change the output from say a typical  eight-bit converter (256 bits) to levels of my own choosing.   How do I go about creating a look-up table to do this?

  • 9. Re: Have a question about ADCs or DACs? Ask our Expert, Nick Gray
    kdboyce e14 Expert

    Hi Nathan,

     

    Let me make clear from the beginning...I am not Nick :>)  I am sure he will reply with a well thought out answer.

     

    However, being in the audio business, your post caught my attention.

     

    My immediate response is to use an associative or content addressable memory.  There are not many simple AM or CAM devices on the market. Those that are one the market are more sophisticated and typically used in high speed search and pattern matching applications.

     

    Since you say you have only an 8 bit converter and need only 256 bits, one could take a small EPROM that had an 8 bit address bus and for each address location program the EPROM memory at that location with whatever HOH data you wanted instead the data at the A-D output.  For each possible A-D value, you could then have an alternative HOH value stored in EPROM memory which would be output to the digital amplifier instead.

     

    You would use a standard EPROM programmer for this task. 

     

    In operation, you would wire the EPROM to output data synchronously with the output rate of the A-D.  Depending upon the converter used, there should be an output synchronous with the 8-bit output.  That synchronous output would be used to enable the READ operation on the EPROM.  It would probably have to be delayed so that it would only cause the EPROM output after the A-D outputs were stable on the EPROM address lines. Otherwise, you might introduce data changes to the audio amplifier which would be basically interpreted as noise.  The delay sould be on the order of microseconds, not milliseconds.

     

    You could try this out on a bench setup, and if the HOH data were fairly consistent over a large group of listeners, you may be able to put the HOH data in a custom memory chip (if production volumes are high enough), or put it in one time programmable ROM, or even a small FPGA.

     

    Good Luck,

    Ken

  • 10. Re: Have a question about ADCs or DACs? Ask our Expert, Nick Gray
    nickgray e14 Expert
    I am sorry, but I am not sure just what kind of "help" you need because the part types are indicated on the schematic. U1 is a "7805" type linear regulator, U2 is a "MAX232", J2 is what is known as a "DB9" connector which is used for RS-232RS-232 interfaces and J1 appears to be a header to connect to whatever is sending and receiving data over the RS-232RS-232 port.

    The 7805 comes in TO-3, TO-220, TO-263 and SOT-223 packages. I believe that any of these packages would be satisfactory, but the SOT-223 and TO-263 packages MIGHT not handle the power requirements of this circuit (max 105mW) without care in how it is mounted. See the data sheet for proper mounting considerations. The TO-220 package should have no problems with power dissipation. Furthermore, I would prefer the LM340 because its specification shows a a little tighter tolerance on the output voltage. Data sheet is at http://www.national.com/ds/LM/LM340.pdf.

    The MAX232 was first introduced by Maxim Integrated Products, but is now available from other semiconductor manufacturers and is available in 16-pin plastic DOP and SOIC. C2 and C3 are used for the on-chip voltage multiplier to boost the +5V from the 7805 or LM340 to +12V and -12V. Data sheet is at http://datasheets.maxim-ic.com/en/ds/MAX220-MAX249.pdf.

    If none of this answers your questions, please clarify just what you need and I will try to provide your answers.
  • 11. Re: Have a question about ADCs or DACs? Ask our Expert, Nick Gray
    nickgray e14 Expert
    I am sorry, but I am not sure just what kind of "help" you need because the part types are indicated on the schematic. U1 is a "7805" type linear regulator, U2 is a "MAX232", J2 is what is known as a "DB9" connector which is used for RS-232RS-232 interfaces and J1 appears to be a header to connect to whatever is sending and receiving data over the RS-232RS-232 port.

    The 7805 comes in TO-3, TO-220, TO-263 and SOT-223 packages. I believe that any of these packages would be satisfactory, but the SOT-223 and TO-263 packages MIGHT not handle the power requirements of this circuit (max 105mW) without care in how it is mounted. See the data sheet for proper mounting considerations. The TO-220 package should have no problems with power dissipation. Furthermore, I would prefer the LM340 because its specification shows a a little tighter tolerance on the output voltage. Data sheet is at http://www.national.com/ds/LM/LM340.pdf.

    The MAX232 was first introduced by Maxim Integrated Products, but is now available from other semiconductor manufacturers and is available in 16-pin plastic DOP and SOIC. C2 and C3 are used for the on-chip voltage multiplier to boost the +5V from the 7805 or LM340 to +12V and -12V. Data sheet is at http://datasheets.maxim-ic.com/en/ds/MAX220-MAX249.pdf.

    If none of this answers your questions, please clarify just what you need and I will try to provide your answers.
  • 12. Re: Have a question about ADCs or DACs? Ask our Expert, Nick Gray
    nickgray e14 Expert
    I am sorry, but I am not sure just what kind of "help" you need because the part types are indicated on the schematic. U1 is a "7805" type linear regulator, U2 is a "MAX232", J2 is what is known as a "DB9" connector which is used for RS-232RS-232 interfaces and J1 appears to be a header to connect to whatever is sending and receiving data over the RS-232RS-232 port.

    The 7805 comes in TO-3, TO-220, TO-263 and SOT-223 packages. I believe that any of these packages would be satisfactory, but the SOT-223 and TO-263 packages MIGHT not handle the power requirements of this circuit (max 105mW) without care in how it is mounted. See the data sheet for proper mounting considerations. The TO-220 package should have no problems with power dissipation. Furthermore, I would prefer the LM340 because its specification shows a a little tighter tolerance on the output voltage. Data sheet is at http://www.national.com/ds/LM/LM340.pdf.

    The MAX232 was first introduced by Maxim Integrated Products, but is now available from other semiconductor manufacturers and is available in 16-pin plastic DOP and SOIC. C2 and C3 are used for the on-chip voltage multiplier to boost the +5V from the 7805 or LM340 to +12V and -12V. Data sheet is at http://datasheets.maxim-ic.com/en/ds/MAX220-MAX249.pdf.

    If none of this answers your questions, please clarify just what you need and I will try to provide your answers.
  • 13. Re: Have a question about ADCs or DACs? Ask our Expert, Nick Gray
    nickgray e14 Expert
    I am sorry, but I am not sure just what kind of "help" you need because the part types are indicated on the schematic. U1 is a "7805" type linear regulator, U2 is a "MAX232", J2 is what is known as a "DB9" connector which is used for RS-232RS-232 interfaces and J1 appears to be a header to connect to whatever is sending and receiving data over the RS-232RS-232 port.

    The 7805 comes in TO-3, TO-220, TO-263 and SOT-223 packages. I believe that any of these packages would be satisfactory, but the SOT-223 and TO-263 packages MIGHT not handle the power requirements of this circuit (max 105mW) without care in how it is mounted. See the data sheet for proper mounting considerations. The TO-220 package should have no problems with power dissipation. Furthermore, I would prefer the LM340 because its specification shows a a little tighter tolerance on the output voltage. Data sheet is at http://www.national.com/ds/LM/LM340.pdf.

    The MAX232 was first introduced by Maxim Integrated Products, but is now available from other semiconductor manufacturers and is available in 16-pin plastic DOP and SOIC. C2 and C3 are used for the on-chip voltage multiplier to boost the +5V from the 7805 or LM340 to +12V and -12V. Data sheet is at http://datasheets.maxim-ic.com/en/ds/MAX220-MAX249.pdf.

    If none of this answers your questions, please clarify just what you need and I will try to provide your answers.
  • 14. Re: Have a question about ADCs or DACs? Ask our Expert, Nick Gray
    nickgray e14 Expert
    I am sorry, but I am not sure just what kind of "help" you need because the part types are indicated on the schematic. U1 is a "7805" type linear regulator, U2 is a "MAX232", J2 is what is known as a "DB9" connector which is used for RS-232RS-232 interfaces and J1 appears to be a header to connect to whatever is sending and receiving data over the RS-232RS-232 port.

    The 7805 comes in TO-3, TO-220, TO-263 and SOT-223 packages. I believe that any of these packages would be satisfactory, but the SOT-223 and TO-263 packages MIGHT not handle the power requirements of this circuit (max 105mW) without care in how it is mounted. See the data sheet for proper mounting considerations. The TO-220 package should have no problems with power dissipation. Furthermore, I would prefer the LM340 because its specification shows a a little tighter tolerance on the output voltage. Data sheet is at http://www.national.com/ds/LM/LM340.pdf.

    The MAX232 was first introduced by Maxim Integrated Products, but is now available from other semiconductor manufacturers and is available in 16-pin plastic DOP and SOIC. C2 and C3 are used for the on-chip voltage multiplier to boost the +5V from the 7805 or LM340 to +12V and -12V. Data sheet is at http://datasheets.maxim-ic.com/en/ds/MAX220-MAX249.pdf.

    If none of this answers your questions, please clarify just what you need and I will try to provide your answers.
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