ADC Principles and Common Applications
Analog signals are signals that have a continuous mathematical form in the time domain, with signal values continuously varying at different time points. They convey information about continuously changing physical quantities such as temperature, humidity, pressure, length, current, and more. Different types of data need to be converted into corresponding analog signals for transmission.
Digital signals, on the other hand, are signals where both the independent and dependent variables are discrete. They can be understood as signals that are discrete both in the time domain and in amplitude, meaning they are not continuous. Digital signals are stored and processed in computers using binary representation.
Using a processor with a working voltage of 3.3V as an example, it generates rectangular wave electrical signals during its operation, which are either 0V (logic 0) or 3.3V (logic 1). In the physical world, a voltage signal of 1V cannot be directly recognized by the CPU; it must be converted into a digital signal by a device called an ADC before it can be recognized by the CPU.
ADC, short for Analog-to-Digital Converter, plays the role of transforming analog signals that computers cannot directly recognize in the physical world into binary digital signals that can be recognized by the CPU.
The basic working principle of ADC involves sampling and quantization. First, ADC samples the analog signal, which means it measures the value of the analog signal at regular time intervals. Then, the sampled analog signal is quantized, which means it is discretized into a series of discrete numerical values. These numerical values are typically represented in binary.
The resolution of an ADC represents its ability to quantify analog signals with precision. It refers to the number of discrete values that the ADC can represent. Resolution is typically measured in bits, such as 8-bit, 10-bit, 12-bit, and so on. For example, an 8-bit ADC can divide the input range into 2^8 (256) different discrete levels, while a 12-bit ADC can divide it into 2^12 (4096) discrete levels. Higher resolution means that the ADC can more accurately quantify analog signals.
The sampling rate of an ADC is the number of times it samples per second. A higher sampling rate results in a more faithful representation of the original analog signal. According to the Nyquist Sampling Theorem, the sampling rate must be at least twice the maximum frequency of the signal being measured to avoid distortion in the sampled waveform. In practical applications, the sampling frequency is often much higher, sometimes even up to 10 times or more the maximum frequency of the signal being sampled.
The input voltage range of an ADC (Analog-to-Digital Converter) refers to the range of analog signal voltages it can accept. It is typically expressed in voltage units, such as 0V to 5V or -5V to +5V. Ensuring that the input signal does not exceed the ADC’s input range is crucial to avoid signal distortion or damage.
ADCs can be triggered in two main ways: software-triggered and hardware-triggered. In software triggering, the ADC starts the conversion immediately when a conversion command is issued in software. In hardware triggering, the ADC waits for a specified external event to occur before starting the conversion. The choice of triggering method depends on the specific application and requirements.
ADCs find wide-ranging applications in various fields, including data acquisition, sensor interfacing, audio processing, communication systems, and more. They are essential components for converting analog signals into digital format, allowing analog signals to interact with and be processed by digital systems.
ADC Descriptions for Various Platforms
ADCs are typically located on the PMU (Power Management Unit) and are part of the Analog IP. A typical structure diagram of the PMU is shown below:
Application Scenarios
Light Sensor
Materials Needed: EC600U module, light-dependent resistor (e.g., GL5528)
Principle:
The resistance of a light-dependent resistor (LDR) changes with varying light intensity.
When the LDR is exposed to light, its resistance decreases.
When the light intensity decreases or there is no light, the resistance of the LDR increases, which affects the voltage at the test point.
By reading the ADC voltage values, you can calculate the resistance value of the LDR. Based on the relationship between the light intensity and the resistance of the LDR, you can determine the intensity of the light.
The hardware circuit is as shown in the diagram below: R2 is the LDR, R1 is 10K (you can choose the value of R1 based on the specific parameters of the LDR), and the ADC port is the test point connected to the module’s ADC pin.
In this example, you can observe the impact of different light levels on the LDR by printing the ADC-measured voltage values and the resistance values of the LDR.
FAQ
ADC Voltage Range
The input voltage for each ADC interface pin must not exceed its allowed voltage range. When the measured voltage is greater than the input voltage range, it should be first reduced by resistor division before connecting it to the module’s ADC pin.
In cases where the module’s VBAT is not powered, to avoid damaging the module, ADC interfaces should not be directly connected to any input voltage.
ADC Bit Width
ADC bit width refers to how many bits are used to represent the ADC conversion result. A larger bit width results in higher resolution and more precise measurements. For example, if a 1V voltage is converted by a 10-bit ADC, each bit represents 1/1024V. The module’s ADC returns the processed voltage value.
