The Cathode follower oscillator (or differential amplifier oscillator, emitter follower oscillator, source-coupled oscillator or Peltz oscillator) is an
electronic oscillator
An electronic oscillator is an electronic circuit that produces a periodic, oscillating or alternating current (AC) signal, usually a sine wave, square wave or a triangle wave, powered by a direct current (DC) source. Oscillators are found ...
circuit in which the oscillation frequency is determined by a
tuned circuit
An LC circuit, also called a resonant circuit, tank circuit, or tuned circuit, is an electric circuit consisting of an inductor, represented by the letter L, and a capacitor, represented by the letter C, connected together. The circuit can act ...
consisting of
capacitor
In electrical engineering, a capacitor is a device that stores electrical energy by accumulating electric charges on two closely spaced surfaces that are insulated from each other. The capacitor was originally known as the condenser, a term st ...
s and
inductor
An inductor, also called a coil, choke, or reactor, is a Passivity (engineering), passive two-terminal electronic component, electrical component that stores energy in a magnetic field when an electric current flows through it. An inductor typic ...
s, that is, an
LC oscillator
An electronic oscillator is an electronic circuit that produces a periodic, oscillating or alternating current (AC) signal, usually a sine wave, square wave or a triangle wave, powered by a direct current (DC) source. Oscillators are found in ma ...
. This oscillator uses one connection to get a signal from the LC-circuit and feeds an amplified signal back. The amplifier is a
long-tail pair
A differential amplifier is a type of electronic amplifier that amplifies the difference between two input voltages but suppresses any voltage common to the two inputs. It is an analog circuit with two inputs V_\text^- and V_\text^+ and one outp ...
of two
triodes
A triode is an electronic amplifying vacuum tube (or ''thermionic valve'' in British English) consisting of three electrodes inside an evacuated glass envelope: a heated filament or cathode, a grid, and a plate (anode).
Developed from Lee ...
, two p-channel
bipolar transistors
A bipolar junction transistor (BJT) is a type of transistor that uses both electrons and electron holes as charge carriers. In contrast, a unipolar transistor, such as a field-effect transistor (FET), uses only one kind of charge carrier. A ...
or two
junction FETs.
Operation
Triode
In the
Cathode follower oscillator schematic, the long tail amplifier is connected to a tap of the LC-circuit inductance for a light load on the LC-circuit. A grid-leak couples the grid of the left triode to the LC-circuit. The left triode uses common anode circuit which has high input impedance, low output impedance and no voltage amplification. The long-tail resistor couples the two triodes. The right triode uses common grid circuit which has low input impedance, high output impedance and no current amplification. A capacitor at the anode resistor of the right triode couples the amplified signal back to the LC-circuit. At low frequency, both triodes have a phase shift of zero degree.
Bipolar PNP
The Peltz oscillator schematic uses PNP transistors. The LC-circuit L1, C1 is connected to the base of the left transistor (Q1) and to the collector of the right transistor (Q2). Q1 is configured as an
emitter follower
In electronics, a common collector amplifier (also known as an emitter follower) is one of three basic single-stage bipolar junction transistor (BJT) amplifier topologies, typically used as a voltage buffer.
In this circuit, the base termi ...
(common-collector) and Q2 is configured as a
common-base amplifier, providing voltage gain. The emitter follower is coupled to the common-base amplifier through the long-tail resistor R1, providing net gain necessary for oscillation. Oscillation frequency is around 10 MHz with the components shown. The circuit is optimized for low supply voltage and can operate down to around 0.8V.
Simple 5-component oscillator works below 0.8V
/ref> The voltage across the tuned circuit is approximately ±Vbe peak relative to ground.
FET
The source-coupled oscillator uses two junction FET and a LC-circuit to produce a sine wave signal. L1 and C1 are the LC-circuit, J1 is a common drain amplifier, J2 is a common gate amplifier. The grid-leak C2, R2 connects the LC-circuit to J1 input. J1 output is directly connected to J2 input. The long-tail resistor R1 works as a primitive current source. If the current through J1 increases, the current through J2 decreases. The LC-circuit is directly connected to J2 output. The circuit is optimized for low supply voltage.
References
{{Electronic oscillators
Electronic oscillators