Operational Amplifier
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Operational Amplifier
Class A RF Amplifier Application Design
Class-A operation is characterized by a continuous DC collector (or drain) voltage and existing. This class of operation is essential for linear amplifiers with severe linearity requirements like:
- Drivers in SSB transmitters where a 2-tone 3rd-order intermodulation of at the very least -40 dB is necessary
- Drivers in Tv transmitters exactly where the contribution for the gain compression has to be quite low, i.e. not much more than some tenths of a dB
- All stages of Tv transposers. These are tested using a 3-tone signal as well as the 3rd-order intermodulation products should be beneath -55 to -60 dB. The driver stages should only deliver a tiny contribution to the general intermodulation, so they've to operate at even lower efficiency than the final stage (as this really is the only strategy to reduce distortion in class-A).
Even though the theoretical maximum efficiency of a class-A amplifier is 50%, due to linearity requirements, the efficiency inside the first two applications listed above will likely be no much more than about 25%. And in Tv transposers, the efficiency is only about 15% for the final stage as well as much less for the driver stages.
The transistor power acquire in a class-A amplifier is about 3 to 4 dB greater than that in the very same transistor operating in class-B. This really is simply because the conduction period of the drain existing in class-A is 360° and in class-B only 180°(electrical degrees). As a result, the powerful transconductancein class-B is only half that in class-A.
DISTORTION
SSB modulation is primarily used within the HF range: 1.5 to 30 MHz. When testing transistors for this application, Philips utilizes a regular test frequency of 28 MHz. Owing to its variable amplitude, an SSB signal is sensitive to distortion.
TONE INTERMODULATION DISTORTION Check
This is the most widespread distortion check. In this check, two equal-amplitude tones 1 kHz apart are applied to the input with the amplifier beneath test. Practical amplifiers will in no way be completely linear, along with the most significant distortion products they create are the 3rd and 5th order ones, since these are in or very near towards the pass-band. In class-A applications, distortion goods are nearly usually specified relative for the amplitude of a single with the input check tones. As a basic guideline, within the linear region of a class-A amplifier, every single 1 dB reduction of output power minimizes 3rd-order intermodulation distortion by 2 dB.
About the Author
I'm interested in any electronics education. I'm graduated from electronics education in high school and graduate from college in computer science. I love electronics and computer. Radio Frequency Amplifier Circuit, Various Reasons of an Isolation Transformer,
How Is A 741 Operational Amplifier Used In A Comparator Circuit?
Hi there,
If anyone can answer my question then that would be great. Thanks in advance!
Opamps can be used as comparators, although they are not ideal. The LM339, for example, is a better choice.
The basic circuit has one of the inputs connected to a voltage reference and the other to the unknown input. When the input is < the reference, the output is slammed to one of the supply rails (depending on the polarity of the inputs) and when the input is > the reference, the output is slammed to the other supply rails.
A better circuit uses some positive feedback to add hysteresis so that the output does not oscillate with input close to the reference voltage.
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Module - 4 Lecture - 1 Operational Amplifier (Introduction)
