Digital Electronics: Principles, Devices and Applications

Logic Gates and Related Devices 105Figure 4.51Parity check using EX-OR and EX-NOR gates.4.13.4 InverterCMOS inverters are commonly used to build square-wave oscillators for generating clock signals.These clock generators offer good stability, operation over a wide supply voltage range (3–15 V) andfrequency range (1 Hz to in excess of 15 MHz), low power consumption and an easy interface to otherlogic families.The most fundamental circuit is the ring configuration of any odd number of inverters. Figure 4.52shows one such circuit using three inverters. Inverting gates such as NAND and NOR gates can alsobe used instead. This configuration does not make a practical oscillator circuit as its frequency ofoscillation is highly susceptible to variation with temperature, supply voltage and external loading. Thefrequency of oscillation is given by the equationf = 1/2nt p (4.12)where n is the number of inverters and t p is the propagation delay per gate.OutputFigure 4.52Square-wave oscillator using a ring configuration.