![]() ![]() 5.1.7 Two Phase Clock Waveforms Circuit Capacitanceīecause the clock must feed many gates, the small capacitance of each of these gates will add, to become an appreciable capacitance, which loads the clock output tending to slow the rise and fall time of the clock signal. ![]() The waveform should be kept as close as possible to a perfect square wave shape.įig. ![]() Also, by maintaining fast rise and fall times, ringing on the waveform can become a problem. Whatever circuit is used to generate a clock signal, it is important that its output has sufficient fan-out capability to drive the necessary number of ICs requiring a clock input, and that the clock signal is not degraded in amplitude, speed of its rise and fall times or accuracy of its frequency. Distributing Clock Signalsįor more demanding applications there are very many specialised clock oscillator ICs available that are typically optimised for a particular range of applications, such as computer hardware, wireless communications, automotive or medical applications etc. If positive going clock pulses are required, the outputs from the NAND gates may be inverted using Schmitt inverters, which will also help to sharpen the rise and fall times of the clock waveforms. Typical output waveforms are illustrated in Fig. The NAND gate producing Φ01 therefore creates a logic 0 pulse whenever CK and Q are at logic 1, and the NAND gate producing Φ02 creates a logic 0 pulse whenever CK and Q are at logic 1. Each of the NAND gates will produce a logic 0 output whenever both its inputs are at logic 1. 5.1.6 illustrates the operation of Fig 5.1.5. ![]()
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