On the other hand, the error minimizes as the number of bits is increased. The maximum sampling rates have also been indicated in the table. It is also known as the parallel ADC converter.
It consists of a number of comparators. An encoder circuit is connected at the output of the comparators which gives us binary output. A flash ADC circuit of 3-bits is shown in the figure:. Vref is the reference voltage; if the analog value at the input becomes greater than the reference voltage then the comparator output will be high. Flash converter is the most efficient of all the converters in terms of speed.
But the number of comparators increases as the number of bits increases. We would require 7 comparators for 3-bit and 15 comparators for 4-bits.
This is the weakness of flash ADC. But a flash converter can produce a non-linear output which is an additional advantage. The voltage divider network consists of equal-value resistors which provide a proportional response. But for special applications, the value of the resistors can be changed which will give a non linear response. A dual slope integrator first integrates and then disintegrates a voltage signal.
It integrates an unknown voltage for a fixed time and disintegrates for variable time using a reference voltage. Figure 5 shows the graph of dual slope integration. The main advantage is that the error occurring in a component during the integration is cancelled out during the phase of de-integration. One way to get this task done is to do a burst of conversions in a row for all your analog channels. Here is a typical implementation for a burst conversion routine. You can just attenuate the original signal by using a proper attenuator or maybe a voltage divider!
Just Apply Voltage Divider Rule. What you should notice is the fact that the accuracy is dropping significantly as we go up. Sometimes a simple common emitter amplifier will do the trick. Even an op-amp can do much help. However, sometimes you may need something different.
Here is an example, instead of trying to measure too very small signals to check the difference between them. You just can use a differential amplifier and amplify this difference between the signals.
Now the job of our ADC is much easier than before! And so on…. Then the analog corresponding voltage is calculated as shown below. Was this helpful for you? Why not share it with your network! Sharing is the best way for supporting free technical content like this,. I love reading, writing, creating projects and Technical training. A reader by day a writer by night, it's my lifestyle. You can view my profile or follow me via contacts. October 26, August 7, August 22, In the first example I have tried i am really confused on how you are directly giving the 10 bit ADC value to Duty cycle, I know that duty cycle is also 10 bit but it is maxing out around scale.
The rest of code is the same until half of the POT the duty changes as expected, but beyond that it becomes messy waveform. Please help…. Well,if that is the case for your program you can right shift the AD-result once so you can fit in the 9bit duty cycle. The resolution for pwm duty cycle is bot fixed. Maybe 8bits or something depending on the exact freq value using the resolution formula you can find that easily. I know that this is not the actual way to approach the mapping Could you tell me a better way to map the ADC values to the PWM equivalent without using a cascade of if else loops….
Just look at the figure where i did deduce the mapping formula for the case of that lab. I have a question about the following portion of the coding, if you can explain this portion to me. Hello Khaled. From what I understand,if the expression inside the parenthesis evaluates to 0, then compiler does not go to the next line of code and waits until this expression inside the parenthesis evaluates to 1.
İf expression evaluates to one it continues to execute the next lines. Coding 8. Simulation 8. Coding 9. ADC Chip. ADC Block Diagram. Sample And Hold Circuit. Like this: Like Loading There are some basic reasons to use digital signals instead of analog, noise being the number one. Since analog signals can assume any value, noise is interpreted as being part of the original signal. Digital systems, on the other hand, can only understand two numbers, zero and one.
Anything different from this is discarded. Another advantage of digital system against analog is the data compression capability. This can be prevented by using an ADC with a higher resolution. ADCs up to 24 bits are available, though conversion frequencies are low, in the order of a few hertz. The number of analog to digital conversions the converter can make every second is called the sample speed. This is to be read as megasamples per second, meaning a million samples per second.
Note that SI prefixes apply here. Sample speed depends completely on the type of converter and the needed accuracy. If a very accurate reading is needed, the ADC usually spends more time looking at the input signal usually a sample-and-hold or integrating type input , and if accuracy is not a concern they can be quick and dirty with the reading.
The general rule of thumb is, speed and accuracy are more or less inversely proportional, it is important to select an ADC depending on the application. This is the simplest type of ADC and as the name suggests the fastest. It consists of a series of comparators with the non-inverting inputs connected to the signal input and the inverting pins connected to a voltage divider ladder.
However, if the voltage is above one of the levels of the ladder, all the output bits below the level are set to one, since the voltage is above the threshold for the bottom comparators.
To circumvent this problem, outputs are fed through a priority encoder that converts the output to binary. The speed is limited only by the propagation delays of the comparator and the priority encoder. However, accuracy is moderate. Here, a ramp generating circuit is started at the time of conversion and a binary counter is started at the same time. A comparator detects when the ramp goes above the input voltage and stops the binary counter.
The binary count obtained is proportional to the input voltage level.
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