Cathode follower oscillator

Cathode follower oscillator

Peltz oscillator

The Cathode follower oscillator is an electronic oscillator circuit in which the oscillation frequency is determined by a tuned circuit consisting of capacitors and inductors, that is, an LC oscillator. The circuit is also known as differential amplifier oscillator, emitter follower oscillator , source-coupled oscillator or Peltz oscillator. 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 of two triodes, two bipolar transistors or two junction FETs.

Operation

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.

The Peltz oscillator schematic uses pnp transistors. The LC-circuit L1, C1 is connected to the base of the left transistor and to the collector of the right transistor. Both transistors are coupled through the long-tail resistor R1. Oscillation frequency is around 10 MHz. The circuit is optimized for low supply voltage.