Input Impedance

Definition

Input impedance is the measure of resistance that an electronic circuit presents to an incoming signal at its input. It is a critical parameter in circuit design, as it affects how signals are transferred between different stages of a system, especially during the process of converting analog signals to digital format.

5 Must Know Facts For Your Next Test

1. Input impedance is typically expressed in ohms and should ideally be much higher than the source impedance to minimize signal loss.
2. In an analog-to-digital converter (ADC), high input impedance allows the ADC to sample signals without loading down the source, preserving signal integrity.
3. Low input impedance can cause distortion or attenuation of the signal being measured, which can lead to inaccurate digital representations.
4. Different types of sensors and sources have varying input impedance characteristics, which need to be matched appropriately for optimal performance.
5. In applications where precise measurements are critical, such as in medical devices or instrumentation, ensuring proper input impedance is essential to achieve reliable results.

Review Questions

• How does input impedance affect signal integrity when interfacing an ADC with a sensor?
  • Input impedance plays a crucial role in maintaining signal integrity during the interfacing of an ADC with a sensor. If the input impedance of the ADC is significantly higher than that of the sensor, it minimizes any loading effect, allowing the sensor's output signal to remain accurate. Conversely, if the ADC's input impedance is low compared to the sensor's output impedance, it may distort or attenuate the signal, leading to erroneous digital conversion.
• What are the implications of low input impedance in an ADC circuit when measuring high-frequency signals?
  • Low input impedance in an ADC circuit can severely impact the measurement of high-frequency signals. It can introduce significant distortion and attenuation due to insufficient charge transfer during rapid signal changes. This mismatch may result in inaccurate sampling and ultimately lead to a failure in capturing the true characteristics of the high-frequency signal being measured.
• Evaluate how selecting components with appropriate input impedances can enhance overall system performance in embedded systems.
  • Selecting components with appropriate input impedances can greatly enhance overall system performance by ensuring effective signal transfer and minimizing distortion. For instance, when connecting sensors to an ADC, choosing an ADC with high input impedance relative to the sensor's output ensures accurate readings without loading effects. This careful consideration leads to improved accuracy and reliability in data acquisition systems, which is vital for applications such as industrial control systems and medical diagnostics.

Related terms

Output Impedance: The impedance that a circuit presents at its output terminal, influencing how it interacts with the load connected to it.

Voltage Divider: A simple circuit that produces an output voltage that is a fraction of its input voltage, often influenced by the input and output impedances of the connected components.

Nyquist Theorem: A principle that determines the minimum sampling rate needed for an analog signal to be converted accurately into a digital signal, which can be affected by the input impedance of the ADC.