Crowbar: The metaphor used to describe the action of an SCR when it is used to protect a load against supply overvoltage.

Critical Frequency: Also known as the cutoff frequency, break frequency, corner frequency, etc. This is the frequency where the total resistance of an RC circuit equals the total capacitive reactance.

Covalent Bond: The shared electrons between the silicon atoms in a crystal represent covalent bonds because the adjacent silicon atoms pull on the shared electrons, just as two tug-of-war teams pull on a rope.

Coupling Circuit: A circuit that couples a signal from a generator to a load. The capacitor is in series with the Thevenin resistance of the generator and the load resistance.

Coupling Capacitor: A capacitor used to transmit an ac signal from one node to another.

Complementary MOS (CMOS): A method of reducing the current drain of a digital circuit by combining n-channel and p-channel MOSFETs.

Compensating Diodes: These are the diodes used in a class B push-pull emitter follower. These diodes have current-voltage curves that match those of the emitter diodes. Because of this, the diodes compensate for changes in temperature.

Compensating Capacitor: A capacitor inside an op amp that prevents oscillations. Also, any capacitor that stabilizes an amplifier with a negative-feedback path. Without this capacitor, the amplifier will oscillate. The compensating capacitor produces a low critical frequency and decreases the voltage gain at a rate of 20 dB per decade above the midband. At the unity-gain frequency, the phase shift is in the vicinity of 270°. When the phase shift reaches 360°, the voltage gain is less than 1 and oscillations are impossible.

Comparator: A circuit or device that detects when the input voltage is greater than a predetermined limit. The output is either a low or a high voltage. The predetermined limit is called the trip point.

Common-Source (CS) Amplifier: A JFET amplifier in which the signal is coupled directly into the gate and all of the ac input voltage appears between the gate and the source, producing an amplified and inverted ac output voltage.

Common-Mode Signal: A signal that is applied with equal strength to both inputs of a diff amp or an op amp.

Common-Mode Rejection Ratio (CMRR): The ratio of differential gain to common-mode gain in an amplifier. It is a measure of the ability to reject a common-mode signal and is usually expressed in decibels.

Common-Emitter Circuit: A transistor circuit where the emitter is common or grounded.

Common-Collector Amplifier: This is an amplifier whose collector is at ac ground. The signal goes into the base and comes out of the emitter.

Common Base (CB): An amplifier configuration in which the input signal is fed into the emitter terminal and the output signal is taken from the collector terminal.