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Most frequency counters work by using a counter, which accumulates the number of events occurring within a specific period of time.After a preset period known as the gate time (1 second, for example), the value in the counter is transferred to a display, and the counter is reset to zero.
A frequency divider, also called a clock divider or scaler or prescaler, is a circuit that takes an input signal of a frequency, , and generates an output signal of a frequency: f o u t = f i n N {\displaystyle f_{out}={\frac {f_{in}}{N}}}
A prescaler is an electronic counting circuit used to reduce a high frequency electrical signal to a lower frequency by integer division.The prescaler takes the basic timer clock frequency (which may be the CPU clock frequency or may be some higher or lower frequency) and divides it by some value before feeding it to the timer, according to how the prescaler register(s) are configured.
Block diagram of Intel 8253. The timer has three counters, numbered 0 to 2. [7] Each channel can be programmed to operate in one of six modes. Once programmed, the channels operate independently. [1] Each counter has two input pins – "CLK" (clock input) and "GATE" – and one pin, "OUT", for data
A gated SR latch circuit diagram constructed from AND gates (on left) and NOR gates (on right) A gated SR latch can be made by adding a second level of NAND gates to an inverted SR latch. The extra NAND gates further invert the inputs so a SR latch becomes a gated SR latch (a SR latch would transform into a gated SR latch with inverted enable).
A phase-locked loop or phase lock loop (PLL) is a control system that generates an output signal whose phase is fixed relative to the phase of an input signal. Keeping the input and output phase in lockstep also implies keeping the input and output frequencies the same, thus a phase-locked loop can also track an input frequency.
Figure 1 - Direct Digital Synthesizer block diagram. A basic Direct Digital Synthesizer consists of a frequency reference (often a crystal or SAW oscillator), a numerically controlled oscillator (NCO) and a digital-to-analog converter (DAC) [5] as shown in Figure 1.
The block diagram below shows the basic elements and arrangement of a PLL based frequency synthesizer. Block diagram of a common type of PLL synthesizer. The key to the ability of a frequency synthesizer to generate multiple frequencies is the divider placed between the output and the feedback input.