Frequency Gen. HF Amplifier Circuit

Discussion in 'The Projects Forum' started by SteTrat, Jan 9, 2016.

  1. SteTrat

    Thread Starter New Member

    Jan 6, 2016
    Hi all,

    This is my first post and as background Information, i am a Msc Chemist student with no electronics education.
    During my Msc Thesis i had to deal with equivalent circuits, Ltspice and impedance spectroscopy, which is quite easy now for me to understand.
    But everything beyond that, i have no idea what´s going in a circuit.

    At the moment i am dealing with this project: adapted from
    It is a Frequency Generator Amplifier with the following specs:

    Amplification: ~ 20db
    max Voltage Output: ~10 V
    max Current Output: ~ 300 mA
    Frequency Range: -3db @ ~10Mhz

    My goal is it to build this.
    But what do i need to be aware of?

    - Heat managment, is a heatsink required for some components ?
    - EM-Radiation, a faradaic enclosure, because i have no idea if this acts like an antenna, and i dont want someone to knock at the door...
    - The Power supply, is this bipolar and how can it be realized ?

    -Anything else ?

    Greets from Austria
  2. GopherT

    AAC Fanatic!

    Nov 23, 2012
    Welcome to the site. Nice to see another chemist joining me.

    What you show is a mid-grade, medium power, "power amplifier" intended for fairly high frequencies and gain of 10.

    The basic layout is the same as the 12 W RMS amplifier from an old TAB electronics book. That book goes into detail about what every transistor, resistor and capacitor does. After you get through the 12 W amplifier, then you can read through the detail of a 100 W amp that is deemed "professional Grade".

    I recommend you buy the book, should be available used on eBay.

    In summary, from left to right, you have two transistors that make a "differential amplifier" and output is sent to a third transistor that acts as a Class A amplifier. The collector of that class A is connected to another transistor and Red LED. That transistor and LED make a constant current source to feed the Class A amplifier which greatly reduces distortion in the class A amp.

    The last stage of transistors is a class AB amplifier (push/pull amplifier). The diodes on the Class A section bias the push/pull output stage. The push/pull outputs has the high power transistors. That output also has resistors connecting back to the differential input. This is called feedback and controls the gain and insures the signal tracks the waveform of the input, essentially correcting for differentials in the output load or gain (Hf) of the specific transistors you have.

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    Last edited: Jan 9, 2016
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