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    ADA4870 as a small linear amplifier with single ended VCC?

    Hello, I happen to have one ADA4870 and these devices can greatly simplify amplification without the use of output transformers.
    I am interested in building a broadband little linear amplifier from a few KHz up to 30MHz and even 50MHz if possible with this device. Output power should be the in the area of 1-5W at 50R.

    It would help me if you could let me know about how much RF power input would cause a 1-5W output?

    Now I have found this document https://www.analog.com/en/analog-dia...generator.html which describes the different configurations but the ADA4870 needs +/-20v.
    Since I only need a couple of watts of RF power out of it, I wonder how can I bias it for single ended 12v operation?
    Professional engineering is the top, but amateur engineering is more fun.
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    Re: ADA4870 as a small linear amplifier with single ended VCC?

    I doubt it will work well as an RF power amplifier. It is really intended as a pulse power driver for MOSFETs and the likes. It has almost no gain and a very low output impedance so you would need a matching network at the output and to drive it with as much voltage as you need at the output pin. It may not work below the specified +5V/-5V supplies and it WILL run very hot, you need to take special care to bond the metal tab under the device to a good heat sink.

    Brian.
    PLEASE - no friends requests or private emails, I simply don't have time to reply to them all.
    It's better to share your questions and answers on Edaboard so we can all benefit from each others experiences.


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    Re: ADA4870 as a small linear amplifier with single ended VCC?

    Quote Originally Posted by betwixt View Post
    I doubt it will work well as an RF power amplifier. It is really intended as a pulse power driver for MOSFETs and the likes. It has almost no gain and a very low output impedance so you would need a matching network at the output and to drive it with as much voltage as you need at the output pin. It may not work below the specified +5V/-5V supplies and it WILL run very hot, you need to take special care to bond the metal tab under the device to a good heat sink.

    Brian.
    Ok, you saved me lots of time of experimenting with this Brian..
    The other alternative I consider is the last circuit from this page http://www.qrp4u.de/docs/en/rf_ampl/index.htm
    But this is a single bander. Although the output transformer counts as a rough BPF too, which is good for both reducing harmonics, but it needs switching between bands.
    Considering this last circuit, I wonder, can I take the Receive output from the tap point of the output transformer through a coupling capacitor, when the transceiver is in receive state, so that I can benefit from this BPF on RX?
    Professional engineering is the top, but amateur engineering is more fun.
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    Re: ADA4870 as a small linear amplifier with single ended VCC?

    These types of amplifiers cannot reach "W" range Power Levels.There are tons of DC to .. RF Power Amplifiers which are able to drive 5W@50 Ohm
    Are you looking for an off-the-shelf RF Power Amplifier ?? Or you would like to build your PA by yourself ??



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    Re: ADA4870 as a small linear amplifier with single ended VCC?

    Quote Originally Posted by BigBoss View Post
    These types of amplifiers cannot reach "W" range Power Levels.There are tons of DC to .. RF Power Amplifiers which are able to drive 5W@50 Ohm
    Are you looking for an off-the-shelf RF Power Amplifier ?? Or you would like to build your PA by yourself ??
    I wanted to investigate a transformer-less design and one that would be able to produce 1-5w without lots of components. I knew this was not quite possible, but this IC seemed initially promisable. The article states 16W at some point could it be true?
    Professional engineering is the top, but amateur engineering is more fun.
    It is when you cross the barrier between these two, that things become really fascinating!



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    Re: ADA4870 as a small linear amplifier with single ended VCC?

    Simple calculation, maximum output swing for bipolar supply is +/- (Vs - 2V). Calculate undistorted Vrms, output power. Maximum output into 50 ohm is about 3.5 W with +/- 20V. Single supply +12V gives less than 0.2 W. Notice that the datasheet examples are for RL 16 to 25 ohms.

    1 - 5 W with 12V supply isn't feasible without transformer.


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    Re: ADA4870 as a small linear amplifier with single ended VCC?

    Quote Originally Posted by FvM View Post
    Simple calculation, maximum output swing for bipolar supply is +/- (Vs - 2V). Calculate undistorted Vrms, output power. Maximum output into 50 ohm is about 3.5 W with +/- 20V. Single supply +12V gives less than 0.2 W. Notice that the datasheet examples are for RL 16 to 25 ohms.

    1 - 5 W with 12V supply isn't feasible without transformer.
    All right, perfectly clear.
    Thank you very much.
    Professional engineering is the top, but amateur engineering is more fun.
    It is when you cross the barrier between these two, that things become really fascinating!



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