Linking gates with capacitors

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Linking gates with capacitors Fig. 45.30 shows a single transistor NOT gate or inverter. The input chain to it contains a capacitor. When switches S, and S2 are open, the transistor base is linked to the power supply positive line through the resistor R, the transistor is on and its output voltage is low. If switch S, is […]

The astable multivibrator

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The astable multivibrator A multivibrator circuit containing resistors is a basic memory element. But the two transistor switches in such a circuit can also be linked by capacitors. Their behaviour will be different because the current through a capacitor is not constant. As the plates of the capacitor become charged, the potential difference between them increases. This voltage […]

Bistable circuits

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Bistable circuits Logic gates can be used to solve logic problems. But with one extra feature feedback- they can do much more. The word ‘feedback’ is a good one to describe this type of connection. The output of a circuit is fed back to the input. Fig. 45.26 shows one example of this with two single transistor NOT […]

Combinational logic

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Combinational logic Often quite a large number of gates are used to solve a particular problem. When used together they make up a combinational logic circuit. You can use any of the fives gates to solve such a logic problem. In many circuits the NAND gate is used as the basic ‘building block’. All the other gates […]

Two inputs to the NOR gate

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Two inputs to the NOR gate With two inputs to a gate (see Fig. 45.21), the truth table is more complicated. There are four ways of connecting high and low voltages to the two inputs. According to the two switch positions, the inputs at A and B can be: both 0, °and I, 1 and 0, or […]

The NOT gate or inverter

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The NOT gate or inverter A single transistor can be used as a NOT gate. This is the simplest type of logic gate. Many such gates, linked together, are used in digital electronic devices like clocks, computers and counters. The gate output voltage is NOT the same as the input voltage. Fig. 45.19 shows one version of such […]

Logic gates

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Logic gates Transistors are often used in digital circuits as logic gates. Here the output is either a high voltage or a low voltage, depending on the voltage values at the inputs to the circuit. There are five basic types of logic gate.