Logic - Translators, Level Shifters： A Semiconductor Device on A Circuit

Logic level converters, or voltage level converters, are used to convert signals from one logic level to another. Today, most systems operate at 3.3V or 5V. A logic level is simply the high or low voltage level of a particular board or integrated circuit. Knowing this, a logic level converter is needed to create a path between processors, sensors, or boards with different voltage levels.

How Does A Transducer IC Work?

Converter ICs provide an interface between components that operate at different voltage levels. They can convert from low to high voltages and vice versa. Both upward and downward logic level conversion is done by selecting the power supply levels VDD (voltage drain) and VCC (voltage common collector). the VCC level sets the input signal level, while VDD selects the output voltage level.

Types of IC Translators

IC translators are available in various pin counts, translation methods, and package types such as SOIC SOT-23, VSSOP, and different logic levels.

Another type of translator is the I2C (interconnect circuit) translator. These are multi-master to multi-slave two-wire serial bus standards capable of serial communication at multiple-bit rates. the signal of an I2C translator consists of a single data signal with a logical level, verified by a clock signal. Both signals being transmitted are bidirectional.

Common Logic Levels And Usage Times

Currently, the three most common logic levels are 1.8 V, 3.3 V, and 5 V. For logic with a single transistor, such as an EMERGENCY gate, we need to apply a voltage above 0.7 V to the base of that transistor to activate it. Thus, for a single-transistor logic, a voltage above 0.7 V is logic 1 and a voltage below 0.7 V is logic 0.

Now, when one transistor is used to drive another transistor, we have to double the voltage over the single transistor. So the threshold voltage here would be 1.4 V. Another example is DTL (diode transistor logic). A diode has a forward voltage drop of 0.7V, so we need 1.4V to activate the circuit. A good margin is safe, so these circuits retain 1.8V by default.

In order for more transistors to perform a task, a higher voltage level is needed, i.e. 3V or 5V. Therefore, the processor or board has different voltage levels, and all these boards, processors, or sensors must coexist in different applications, which can be achieved by forming logic-level conversion bridges.

Almost all the cards and sensors of the new series operate at a 3.3V logic level. If they are to be connected to a 5V board like the Arduino UNO, voltage conversion is required. However, in some cases, we don't need conversion circuits to connect two boards with different voltage levels.

We all know that from basic electronics, for most boards, most of the time voltage levels above 2V are logic 1 and voltage levels below 0.8V are logic 0. So with this, we can easily apply 3.3V signals to 5V processors/cards without additional circuitry. But of course, it is necessary to check the threshold voltage level in the datasheet of the IC used.

How to Design A 5 V - 3.3 V Conversion Circuit ?

For inverting conversion, a dual-transistor logic is required. Two transistors are connected in series inverting to obtain a non-inverting +5V output. When 3.3V is applied to the first transistor, it saturates and gives an inverted signal to the second transistor, which inverts its level again to give a +5V signal at the output. It should also be understood that a low drop output very close to +5V can be obtained by using an N-channel MOSFET instead of an NPN transistor in Q2, taking into account the voltage drop across resistor R2.

Bidirectional Logic Level Shifter Circuit

A simple bidirectional logic level converter is a very convenient and fast circuit because it is built around a transistor and switching speed is not an issue.

When HIGH (pin) is a logic 1 (i.e., 5 volts at this pin), the drain and source of the MOSFET are pulled high. In this case, the gate voltage is lower than the source voltage, which puts the MOSFET in the cutoff region (i.e., inactive). Therefore, the LOW pin is pulled to 3.3 volts because no current flows through the gate. When High is a logic 0, the gate voltage is greater than the source voltage, resulting in a lower output on the LOW pin.

Similarly, when LOW is a logic 1, Vgs (the gate-to-source voltage) becomes zero, causing the transistor to become inactive, pulling the HIGH pin to +5 volts. When LOW is a logic 0, the gate voltage is again higher than the source voltage, pulling the HIGH pin low.

In this article, we've discussed logic-level converters, looking at why and when they are needed. We've looked at some conversion circuits and a few ICs for multi-line conversion.

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