Doherty amplifier
Encyclopedia
The Doherty amplifier is a modified class C radio frequency
amplifier
invented by William H. Doherty
in 1936.
The amplifier is usually configured as a grounded-cathode, carrier-peak amplifier. Using two vacuum tube
s, or two power transistors in modern implementations, one as a carrier tube and the other as a peak tube, the amplifier operates by cutting off the negative swing of the RF wave and adding it to the positive swing, greatly improving efficiency and wasting less energy than earlier plate-modulated RF amplifiers.
The amplifier's response is more linear than earlier designs, allowing it to respond to variations in RF power from the modulator more efficiently. Because the voltage and current of both tubes are present on the load, the amplifier constantly sees a varying load, which caused problems in early Doherty designs in balancing the tubes as early engineers didn't fully understand the amplifier's response characteristics. To balance the load more evenly between the carrier and peak tubes, an inductance
is added between the two anodes to stabilize the load, allowing easier tuning of the amplifier.
Radio frequency
Radio frequency is a rate of oscillation in the range of about 3 kHz to 300 GHz, which corresponds to the frequency of radio waves, and the alternating currents which carry radio signals...
amplifier
Amplifier
Generally, an amplifier or simply amp, is a device for increasing the power of a signal.In popular use, the term usually describes an electronic amplifier, in which the input "signal" is usually a voltage or a current. In audio applications, amplifiers drive the loudspeakers used in PA systems to...
invented by William H. Doherty
William H. Doherty
William H. Doherty was an American electrical engineer noted for his invention of the Doherty amplifier....
in 1936.
The amplifier is usually configured as a grounded-cathode, carrier-peak amplifier. Using two vacuum tube
Vacuum tube
In electronics, a vacuum tube, electron tube , or thermionic valve , reduced to simply "tube" or "valve" in everyday parlance, is a device that relies on the flow of electric current through a vacuum...
s, or two power transistors in modern implementations, one as a carrier tube and the other as a peak tube, the amplifier operates by cutting off the negative swing of the RF wave and adding it to the positive swing, greatly improving efficiency and wasting less energy than earlier plate-modulated RF amplifiers.
The amplifier's response is more linear than earlier designs, allowing it to respond to variations in RF power from the modulator more efficiently. Because the voltage and current of both tubes are present on the load, the amplifier constantly sees a varying load, which caused problems in early Doherty designs in balancing the tubes as early engineers didn't fully understand the amplifier's response characteristics. To balance the load more evenly between the carrier and peak tubes, an inductance
Inductor
An inductor is a passive two-terminal electrical component used to store energy in a magnetic field. An inductor's ability to store magnetic energy is measured by its inductance, in units of henries...
is added between the two anodes to stabilize the load, allowing easier tuning of the amplifier.