LOW SCALE INTEGRATION

Low scale integration is a simple way from making a single transistor to putting several transistors on the same chip and linking them into straightforward circuit modules. The fact that the transistors are all on the same chip implies that their characteristics (e.g. gain) are the same. This removes the requirement of match transistors while building a circuit from various individual devices.

The very simple CMOS logic ICs are representative examples of LSI. The figure shown below is the circuit of an inverter.

The inverter comprises 2 MOSFETS, 1 n-channel & one p-channel. Depending on the logic level of the input-A, one or the other of the transistors is switched on. The output is linked to either the +ve supply or the 0 V line. The CMOS4016 IC has 6 such inverters, with individual inputs and outputs, but they have common power line connections .The inverter is part of another CMOS device, the analogue bi-lateral switch.

The switch is constructed from 4 MOSFETs. When the control input is at logic high, both transistors are switched on. Analogue signals can flow in either direction (and this is the reason it is called ‘bilateral’). The 4016 and 4066 ICs consists of 4 switches, each switch has its own control input. These switches can be connected together in a variety of switching configurations, for example, SPDT, DPDT, and many others.