A-Level Physics Specification

AQA 7408

Section 13.5: Digital signal processing

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#13.5.1

Combinational logic

Use of Boolean algebra related to truth tables and logic gates.

\(\bar{a} = \bold{not}~A \)

\(A ⋅ B = A~\bold{and}~B \)

\(A + B = A~\bold{or}~B \)

Identification and use of AND, NAND, OR, NOR, NOT and EOR gates in combination in logic circuits.

Construction and deduction of a logic circuit from a truth table.

The gates should be treated as building blocks. The internal structure or circuit of the gates is not required.

#13.5.2

Sequential logic

Counting circuits:
- Binary counter
- BCD counter
- Johnson counter.

Inputs to the circuits, clock, reset, up/down.

Outputs from the circuits.

Modulo-n counter from basic counter with the logic driving a reset pin.

The gates should be treated as building blocks. The internal structure or circuit of the gates is not required.

#13.5.3

Astables

The astable as an oscillator to provide a clock pulse.

Clock (pulse) rate (frequency), pulse width, period, duty cycle, mark-to-space ratio.

Variation of running frequency using an external RC network.

Knowledge of a particular circuit or a specific device (eg 555 chip) will not be required.