28-06-2012, 02:12 PM
D-Type flip-flop (Toggle switch)
D-Type flip-flop.pdf (Size: 193.48 KB / Downloads: 117)
The D-type flip-flops are used in prescalar/divider circuits and frequency phase detectors. Figure 1 shows how the flip-flop (latch) can be made using 2-input logic circuits and Figure 2 shows the input and output waveforms
The enable pin needs to be high for data to be fed to the outputs Q and Q bar.
The output will only change on the falling edge or trailing edge of the applied clk input.
RF Application
Phase detectors are part of a Phase Locked Loop (PLL) and can be either analogue eg mixer or digital eg D-type flip-flop. When a mixer is used the output consists of the sum and difference frequencies.
In an analogue mixer a number of different frequencies are generated within the mixer namely the sum of the frequencies and the difference frequency (otherwise known as the beatnote) when both input frequencies are the same is the phase difference is zero and the beatnote is DC.
Most PLL circuits now use digital phase detectors formed from two D-type flip-flops as shown in Figure 7.