중앙대학교 전자회로설계실습 Op Amp의 특성측정 방법 및 Integrator 설계

문서 내 토픽

1. Offset Voltage

OP-Amp 내부에 Offset voltage가 존재하므로 출력전압은 0 V가 아니며 그 출력전압을 Open loop gain으로 나누면 Offset voltage를 구할 수 있다. 그러나 실제로는 이런 방법을 사용할 수 없는데, 그 이유는 1번 단자와 2번 단자에 같은 입력전압을 넣으면 Differential 성분이 0이라고 추측하기 쉽지만 실제로는 Op-Amp안의 설계를 보면 Offset-free op amp의 +단자에 가 연결되어있어 정확히 Matching이 되어 있지 않기 때문에 Differential 성분이 0이 아니기 때문이다. 따라서 이를 이용해 Offset Voltage를 구하기에는 어려움이 있다.
2. Offset Voltage 측정방법

이상적인 Op Amp를 사용하여 100 Hz에서 Gain이 100 (V/V), 1000(V/V)인 Inverting Amplifier를 설계하고, 두 회로에 대해 유한한 크기의 open loop gain을 고려하여 이득을 구하기 위한 수식을 제출한다. Op amp의 두 입력 단자를 접지하고 위의 두 회로의 출력전압을 측정하여 수식을 이용하여 offset voltage를 측정하여 구할 수 있다. Data sheet에서 Offset voltage의 min., typ, max. 값은 각각 최솟값, 대푯값, 최댓값을 의미하며, Offset voltage의 경우 0에 가까울수록 이상적인 회로이기 때문에 min의 경우는 따로 지정할 필요성이 없다.
3. Offset Voltage 조정방법

Op Amp의 offset Voltage를 최소화하기 위해서는 1번과 5번 핀이 offset-nulling단자에 해당하는 UA841CN IC의 경우 10 k 의 Potentiometer를 사용하여 Offset voltage의 역할을 상쇄시킬 수 있다.
4. Slew Rate 측정방법

Slew-rate = ( = 최소 주파수)의 식으로 나타낼 수 있으며 출력 파형이 정현파가 아닌 왜곡되어 보이게 되는 때 왜곡될 때의 주파수가 가 된다. Slew를 최소화하기 위해서는 주파수나 입력전압을 낮춰주면 된다.
5. Integrator 설계

입력저항이 530 이며, 4 (-2 V~2 V)의 1 kHz 구형파를 인가했을 때 4 의 삼각파를 출력하는 이상적인 적분기를 설계하고 PSPICE를 이용하여 회로, 입력전압과 출력전압의 파형을 제출한다. Offset voltage가 있을 때, 설계한 적분기의 출력파형은 DC전압을 갖게 되어 고주파수로 갈수록 파형이 점점 올라가는 기울기를 갖는 형태가 될 것이다. Offset voltage에 의한 문제를 해결하기 위하여 DC path( )를 추가하면 되지만, 가 너무 크거나 또는 너무 작으면 각각 연결을 한 게 의미가 없거나 Inverting amplifier의 회로와 같아지게 된다.
6. Miller integrator circuit을 이용한 offset voltage 측정

입력저항이 100 이고 C = 100 인 Miller integrator circuit에 스위치를 커패시터에 병렬로 연결하여 스위치가 끊어지고 난 뒤 5초 후의 값을 통해 offset voltage를 계산할 수 있다. 적분기가 offset voltage로 인해 캐패시터가 충전을 하게 되는데 스위치를 이용해 5초 뒤부터 선형적으로 충전됨을 볼 수 있다.
7. 센서의 출력을 적분하기위한 Integrator 설계

실험 3.2.1 (A)에서 가 추가된 적분기를 설계하고 가 클 때, 적당할 때, 작을 때 나타나는 파형을 제출한다. Input pulse의 크기를 2 V, 주파수를 250 Hz로 설정하고 R = = 1 k , C = 0.47 로 설계하였을 때 입력전압이 인가되고 2 ms뒤에 값이 보이도록 출력파형을 제출한다. 이론과 비교했을 때 차이가 있는데, simulation결과는 삼각파형에서 약간 둥글게 휘어진 파형이 출력됨을 확인할 수 있다.

Easy AI와 토픽 톺아보기

1. Offset Voltage

Offset voltage is an important parameter in analog circuit design, as it can significantly impact the performance and accuracy of the circuit. Offset voltage refers to the voltage that appears at the output of an operational amplifier (op-amp) or other analog device even when the input voltage is zero. This offset voltage can be caused by various factors, such as manufacturing imperfections, temperature variations, and input bias currents. Understanding and minimizing offset voltage is crucial in applications where high precision and accuracy are required, such as in instrumentation, medical devices, and industrial control systems. Proper design techniques, including input offset voltage cancellation, can help reduce the impact of offset voltage and improve the overall performance of the analog circuit.
2. Offset Voltage 측정방법

Measuring offset voltage in analog circuits is an important step in ensuring the proper operation and performance of the circuit. There are several methods for measuring offset voltage, each with its own advantages and disadvantages. The most common methods include: 1. Direct measurement: This involves connecting the op-amp or analog device directly to a voltmeter and measuring the output voltage with zero input. This method is simple but may not account for the effects of loading on the circuit. 2. Null method: In this method, an adjustable voltage source is connected in series with the input of the op-amp or analog device, and the voltage is adjusted until the output is zero. The value of the adjustable voltage source is then the offset voltage. 3. Chopper stabilization: This technique involves periodically reversing the input polarity of the op-amp or analog device, which effectively cancels out the offset voltage. The residual voltage at the output is then the offset voltage. 4. Autozeroing: This method uses a sample-and-hold circuit to periodically measure and store the offset voltage, which is then subtracted from the output to cancel the offset. The choice of measurement method will depend on the specific requirements of the application, the available equipment, and the desired accuracy and precision of the offset voltage measurement.
3. Offset Voltage 조정방법

Adjusting or compensating for offset voltage in analog circuits is an important step in ensuring the proper operation and performance of the circuit. There are several methods for adjusting offset voltage, each with its own advantages and disadvantages: 1. Offset voltage adjustment potentiometer: This involves connecting a potentiometer in series with the input of the op-amp or analog device, allowing the user to manually adjust the offset voltage. 2. Offset voltage nulling: This method involves connecting an adjustable voltage source in series with the input of the op-amp or analog device, and adjusting the voltage until the output is zero. 3. Offset voltage cancellation: This technique involves adding an additional op-amp or analog device in series with the main circuit, with the purpose of cancelling out the offset voltage. 4. Autozeroing: This method uses a sample-and-hold circuit to periodically measure and store the offset voltage, which is then subtracted from the output to cancel the offset. 5. Chopper stabilization: This technique involves periodically reversing the input polarity of the op-amp or analog device, which effectively cancels out the offset voltage. The choice of adjustment method will depend on the specific requirements of the application, the available components, and the desired level of precision and stability. In many cases, a combination of these techniques may be used to achieve the desired level of offset voltage compensation.
4. Slew Rate 측정방법

Slew rate is an important parameter in analog circuit design, as it determines the maximum rate of change of the output voltage of an op-amp or other analog device. Measuring slew rate is crucial in applications where high-speed performance is required, such as in video amplifiers, high-frequency filters, and power electronics. There are several methods for measuring slew rate, each with its own advantages and disadvantages: 1. Step response method: This involves applying a step input to the op-amp or analog device and measuring the time it takes for the output to reach a certain percentage of its final value. The slew rate is then calculated as the change in output voltage divided by the time. 2. Ramp response method: In this method, a linear ramp input is applied to the op-amp or analog device, and the maximum rate of change of the output voltage is measured. 3. Frequency response method: This involves measuring the frequency response of the op-amp or analog device and calculating the slew rate from the high-frequency rolloff. 4. Transient response method: This method involves applying a high-frequency square wave input to the op-amp or analog device and measuring the rise and fall times of the output. The choice of measurement method will depend on the specific requirements of the application, the available equipment, and the desired accuracy and precision of the slew rate measurement. In many cases, a combination of these techniques may be used to obtain a more comprehensive understanding of the slew rate performance of the analog circuit.
5. Integrator 설계

Designing an integrator circuit is an important task in analog circuit design, as integrators are widely used in various applications, such as signal processing, control systems, and instrumentation. The design of an integrator circuit involves several key considerations: 1. Operational amplifier selection: The choice of op-amp is crucial, as it determines the performance characteristics of the integrator, such as input offset voltage, input bias current, and gain-bandwidth product. 2. Capacitor selection: The value of the integrating capacitor determines the gain and time constant of the integrator, which in turn affects the frequency response and stability of the circuit. 3. Feedback resistor selection: The feedback resistor, along with the integrating capacitor, determines the time constant of the integrator, which affects the low-frequency response and the overall stability of the circuit. 4. Input impedance and loading: The input impedance of the integrator and the loading on the output must be considered to ensure proper operation and to avoid loading effects. 5. Offset voltage compensation: Offset voltage in the op-amp can cause the integrator output to drift over time, so offset voltage compensation techniques may be necessary. 6. Stability and frequency response: The design of the integrator must consider the stability and frequency response of the circuit, as these factors can impact the overall performance of the system. By carefully considering these design factors, engineers can create high-performance integrator circuits that are well-suited for a wide range of analog applications.
6. Miller integrator circuit을 이용한 offset voltage 측정

The Miller integrator circuit is a useful technique for measuring offset voltage in analog circuits. This method involves using an op-amp configured as an integrator, with a capacitor connected between the output and the inverting input. The key advantage of the Miller integrator for offset voltage measurement is that it can effectively amplify the offset voltage, making it easier to measure and characterize. The offset voltage at the op-amp input is integrated over time, causing the output voltage to ramp up or down at a rate proportional to the offset voltage. To use the Miller integrator for offset voltage measurement, the following steps are typically followed: 1. Configure the op-amp as an integrator, with a feedback capacitor connected between the output and the inverting input. 2. Apply a known input voltage (typically 0V) to the integrator. 3. Measure the output voltage of the integrator over time, and calculate the rate of change (slope) of the output voltage. 4. The offset voltage can then be calculated from the slope of the output voltage, using the known values of the integrating capacitor and feedback resistor. By using the Miller integrator circuit, the offset voltage can be effectively amplified and measured with high precision, even in the presence of other circuit noise and disturbances. This makes the Miller integrator a valuable tool for characterizing and troubleshooting offset voltage issues in analog circuits.
7. 센서의 출력을 적분하기위한 Integrator 설계

Designing an integrator circuit to integrate the output of a sensor is an important task in many applications, such as position sensing, velocity measurement, and signal processing. The key considerations in designing such an integrator circuit include: 1. Sensor characteristics: Understanding the output characteristics of the sensor, such as the voltage range, impedance, and noise level, is crucial in selecting the appropriate op-amp and other components for the integrator. 2. Op-amp selection: The choice of op-amp is critical, as it determines the input offset voltage, input bias current, gain-bandwidth product, and other performance parameters that can affect the accuracy and stability of the integrator. 3. Integrating capacitor selection: The value of the integrating capacitor determines the gain and time constant of the integrator, which in turn affects the frequency response and stability of the circuit. 4. Feedback resistor selection: The feedback resistor, along with the integrating capacitor, determines the time constant of the integrator, which affects the low-frequency response and the overall stability of the circuit. 5. Input impedance and loading: The input impedance of the integrator and the loading on the output must be considered to ensure proper operation and to avoid loading effects. 6. Offset voltage compensation: Offset voltage in the op-amp can cause the integrator output to drift over time, so offset voltage compensation techniques may be necessary. 7. Stability and frequency response: The design of the integrator must consider the stability and frequency response of the circuit, as these factors can impact the overall performance of the system. By carefully considering these design factors, engineers can create high-performance integrator circuits that can effectively integrate the output of a sensor, providing accurate and reliable measurements for a wide range of applications.

주제 연관 토픽을 확인해 보세요!

주제 연관 리포트도 확인해 보세요!