# In logic levels, why are both the driver and receiver needed?

Here is what my textbook has to say about logic levels:

The mapping of a continuous variable onto a discrete binary variable is done by defining logic levels. [...] The first gate is called the driver and the second gate is called the receiver. The output of the driver is connected to the input of the receiver. The driver produces a LOW (0) output in the range of 0 to VOL or a HIGH (1) output in the range of VOH to VDD. If the receiver gets an input in the range of 0 to VIL, it will consider the input to be LOW. If the receiver gets an input in the range of VIH to VDD, it will consider the input to be HIGH. If, for some reason such as noise or faulty components, the receiver’s input should fall in the forbidden zone between VIL and VIH, the behavior of the gate is unpredictable. VOH, VOL, VIH, and VIL are called the output and input high and low logic levels.

(Digital Design and Computer Architecture - David Harris and Sarah Harris)

Since it seems that the driver itself is able to convert continuous analogue values to discrete ones (HIGH and LOW). Why do we need the receiver as well?

Thank you!

• ... What detector? Jun 2, 2014 at 4:34
• Sorry, I meant driver! Jun 2, 2014 at 4:40

The driver is the output of one logic gate (or flip-flop or other logic devices), and the receiver is the input of another logic gate.

In any system using digital logic, you will have many logic circuits interconnected, with each interconnection having a driver and one or more receivers.

In that description, the driver and receiver are not parts of a single device.

• That's not to say that you couldn't build a single device that would act as both gates together, just that's it's easier to compartmentalize each gate into a discrete unit. Jun 2, 2014 at 5:34

The driver is not a device that maps analog values to binary vaues. The circuit which does this is called analog to digital converter (ADC).

Driver and receiver in digital is similar to source and load in analog. In digital, the information or the logic level, not power, is send from one gate to other. The gate which receives information is called receiver and the first gate which drives the input of receiver to either of the logic level is called driver.

For proper logic transmission, the receiver should understand the logic level voltages produced at output of driver. ie, $V_{OH} > V_{IH}$ and $V_{OL} < V_{IL}$.