quad bilateral switch

bst_14.gif (721 bytes)

Technology: CMOS

Power supply: 3-15 V

14-pin DIL


Pin connections Applications
What is a bilateral switch?
Basic operation LINKS . . .

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Pin connections

4016 pins

The 4016 contains four switches. Each
switch has two input/output terminals,

X and Y and an enable terminal, E.
E is LOW, the switch is open.
E is HIGH, the switch is closed.

Y0-Y3, Z0-Z3: input/output terminals


What is a bilateral switch?

A bilateral switch uses a special CMOS circuit called a transmission gate. The circuit behaves as a SPST (single pole/single throw) switch which is under electronic control. When the control signal, or enable, is HIGH, the switch is closed, allowing signals to be transferred between the switch terminals. The switch is 'bilateral' because either terminal can be used as the input. In other words, current flow can be in either direction.

The ON resistance of 4016 switches is around 300 W.

In digital mode, logic 0 and logic 1 signals are transferred by the 4016 switches. In this mode, the action of the switches can resemble logic gates. For example, if X is used as a switch input, when X=1 AND E=1, output Y=1. This is just like the action of an AND gate.

In analogue mode varying signals, such as audio signals are transferred. This opens up interesting methods for the electronic control of signal transfer. The analogue signal must be kept within the limits set by the power supply to the 4016. If the analogue signal is centred around 0 V, the pin 7 voltage of the 4016 should be connected to a negative voltage, say -5 V, with the pin 14 positive voltage connected to +5 V. Alternatively, a DC voltage can be added to the audio signal so that it remains within the limits of the normal power supply.

Switches can be linked together to provide SPDT (single pole/double throw), DPST (double pole/single throw) and DPDT (double pole/double throw) action:

linking switches

For SPDT and DPDT action, a NOT gate is needed. A transistor NOT gate or a spare gate in another integrated circuit can be used. When enable is LOW input A is connected to output A1. When enable is HIGH, input A is connected to output A2.


Basic operation

It is easy to test the operation of one of the switches inside the 4016:

4016 test circuit

The prototype board layout below shows how to build this circuit:

click for pins! 4016
4016 test circuit

When you press the switch, the LED should illuminate. Once you have made the circuit work, swap the positions of the link wires to Y2 and Z2 and confirm that current can flow in either direction through the switch.

Try modifying the circuit to make SPDT, DPST and DPDT switches.



The more interesting applications of the 4016 take advantage of the fact that analogue signals, like audio signals, can be switched ON and OFF.

One idea for a hearing protection system uses a 4016 switch to 'disconnect' signals to headphones when loud noises occur. A system like this could be useful in industry where workers are exposed to high noise levels, such as pneumatic drills, or for shooting, to protect against the sudden loud noise of a rifle shot. At other times, low level audio signals are amplified and can be heard in the headphones. People can talk to each other without removing the headphones.

The block diagram for a typical audio system includes a sound sensor, preamplifier, audio amplifier (power amplifier) and the headphone speakers:

audio system block diagram

To give electronic control of maximum noise levels, an electronic switch is inserted between the preamplifier and audio amplifier stages:

hearing protection system block diagram

Audio signals from the preamplifier are rectified and smoothed. This gives a DC level which rises and falls in line with the maximum amplitude of the audio signal. When a loud noise occurs, the DC level rises. If this exceeds the threshold level set by the reference level input to the voltage comparator, the electronic switch is switched OFF, preventing signals from reaching the audio amplifier.

This idea was developed through several prototype board stages and was found to work quite well in practice. Here is the circuit diagram:

hearing protection system circuit diagram

A 741 op-amp is suitable for the inverting amplifier stage but a 3130 op-amp is a better choice for the voltage comparator stage. The 3130 has a faster 'slew rate', meaning that its output voltage changes more quickly. In other words, the 3130 reacts more quickly to cut off potentially damaging sounds when the threshold level is exceeded.

The potentiometer connected to the non-inverting input of the 3130 is adjusted to give an appropriate threshold sound level. This is determined by trial and error while listening in the headphones.


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