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--- circuit_design:4_opamp_basic_circuits_ii [2023/09/13 07:39]
mexleadmin [4.3 Instrumentation Amplifier]
+++ circuit_design:4_opamp_basic_circuits_ii [2023/09/19 22:16] (aktuell)
mexleadmin
@@ Zeile 1: / Zeile 1: @@
-====== 4. Basic Circuits II ======
+====== 4 Basic Circuits II ======
 <callout>
@@ Zeile 10: / Zeile 10: @@
 === Introductory Example===
-In various applications, currents must be measured. In an electric motor, for example, the torque is caused by the current flowing through the motor. A motor control and also a simple overcurrent shutdown is based on the knowledge of the current. For further processing, a voltage must be generated from the current. The simplest current-to-voltage converter is the ohmic resistor. A sufficiently large voltage as required by a microcontroller, for example, cannot be achieved with this. So not only the current has to be converted, but also the generated potential difference has to be amplified.
+In various applications, currents must be measured. In an electric motor, for example, the torque is caused by the current flowing through the motor. A motor control and a simple overcurrent shutdown are based on the knowledge of the current. For further processing, a voltage must be generated from the current. The simplest current-to-voltage converter is the ohmic resistor. A sufficiently large voltage as required by a microcontroller, for example, cannot be achieved with this. So not only does the current have to be converted, but also the generated potential difference has to be amplified.
 One such current sense amplifier is the [[http://www.ti.com/lit/ds/symlink/ina240.pdf|INA 240]] device. This is installed as shown below. In the simulation, a real current source feeds the electrotechnical image of a DC motor on the left (in the example: inductance with $L_{\rm L}=10~\rm mH$ and internal resistance $R_{\rm L}=1~\Omega$). The current flowing from the motor is conducted through a measuring resistor ($R_{~\rm M}=0.01~\Omega$) which is noticeably smaller than the internal resistance of the motor. Thus, most of the power acts in the motor and the current is only marginally affected by the sense resistor. The simulation above shows the inner workings of the current measuring amplifier.
@@ Zeile 40: / Zeile 40: @@
 From the [[3_opamp_basic_circuits_i#inverting_amplifier|inverting amplifier]] another circuit can be derived, which can be seen in <imgref pic1>. Here, both the green part of the circuit and the purple part correspond to an inverting amplifier.
-How can $U_\rm O$ be calculated in this circuit? To do this, it is first important to understand what is being sought (compare [[3_opamp_basic_circuits_i#steps_to_the_goal|steps to the goal]]). The goal is to find the relationship between output and input signals: $U_{\rm O}(U_{\rm I1}, U_{\rm I2})$. Different ways to get there were explained in [[electrical_engineering_1:network_analysis|Electrical engineering 1: Network analysis]]. Here we will now outline a different way.
+How can $U_\rm O$ be calculated in this circuit? To do this, it is first important to understand what is being sought (compare [[3_opamp_basic_circuits_i#steps_to_the_goal|steps to the goal]]). The goal is to find the relationship between output and input signals: $U_{\rm O}(U_{\rm I1}, U_{\rm I2})$. Different ways to get there were explained in [[electrical_engineering_1:network_analysis|Electrical engineering 1: Network analysis]]. Here we will outline a different way.
 In the case of a circuit with several sources, superposition is a suitable method, in particular the superposition of the effect of all sources in the circuit. For superposition, it must be ensured that the system behaves linearly. The circuit consists of ohmic resistors and the operational amplifier. These two components give twice the output value when the input value is doubled - they behave linearly. For superposition, the effect of the two visible voltage sources $U_{\rm I1}$ and $U_{\rm I2}$ must be analyzed in the present circuit. \\
@@ Zeile 151: / Zeile 151: @@
 ~~PAGEBREAK~~ ~~CLEARFIX~~
-In <imgref pic4> one can see the circuit of a current-voltage converter. The current-to-voltage converter changes its __output voltage__ based on an __input current__. This circuit is also called a [[https://en.wikipedia.org/wiki/Transimpedance_amplifier|transimpedance amplifier]] because here the transfer resistance - that is, the transimpedance - represents the gain. Generally, the gain was expressed as
+In <imgref pic4> one can see the circuit of a current-voltage converter. The current-to-voltage converter changes its __output voltage__ based on an __input current__. This circuit is also called a [[https://en.wikipedia.org/wiki/Transimpedance_amplifier|transimpedance amplifier]] because here the transfer resistance - that is, the trans-impedance - represents the gain. Generally, the gain was expressed as
 $$A={ {\rm output} \over {\rm input} }$$.
@@ Zeile 160: / Zeile 160: @@
 $R_1$ is the resistor used in the circuit.
-In the simulation, the slider on the right ("Current of current source") can be varied. This changes the input current and thus also the output voltage.
+In the simulation, the slider on the right ("Current of current source") can be varied. This changes the input current and thus the output voltage.
 This circuit can be used, for example, to read a [[https://en.wikipedia.org/wiki/Photodiode|photodiode in volt-free circuit]] ([[https://en.wikipedia.org/wiki/Transimpedance_amplifier|further explanation]] and integrated circuit {{elektronische_schaltungstechnik:tsl250r.pdf}}).
@@ Zeile 191: / Zeile 191: @@
 ~~PAGEBREAK~~ ~~CLEARFIX~~
+====== Applications ======
+===== Programmable Gain Amplifier =====
+Often in applications an analog signal is too small to process (e.g. to digitalize it afterward). \\
+To amplify it an OpAmp can be used. However, for a wide input range, it might be beneficial to have an adjustable scale.
+This can be done with a simple non-inverting amplifier combined with a resistor network as seen in the next simulation. \\
+In this case, a so-called **single-ended** input is used. This means the input voltage is always referred to the ground.
+<WRAP>{{url>https://www.falstad.com/circuit/circuitjs.html?running=false&ctz=CQAgzCAMB0l3AWAnC1b0DYq2QJgRgrgBwDsGpArApEsSJaQyAhJQKYC0AjNwFABDELkpYkWMJVwhxMkN0ogei7vHjZEKSnGqQa3Ghiwwd8tXD4AnFsXrcwWBLflSoM81Zt2M9J3eIIbkhqnn7CcF7C3MbuFtZhuGDSCU5uqhYA7pEKyc7RkFB8WWH52T6FxXkB2UjSkEU1ufS4EfWVzdGRuPgVXT0JSYUA5l2pCaJubeCusgidslNhs3kkvSUO2auLeRgFrNKl23a1LIPcJ4uD3YEJPVNJduTCE9xPRzJYlBuyuA0iWMQCi16IDhHwAG7hOyuYEgUEFPYI2CQRQI7CUPgjWE5KHyN6FUqSA5PMDVV5YbgaSCU9LmeB8Uo0AoGG5nBCBSkmalmOn0xkRWH7XGc5E03n04oRFngMns3qkjlyhXyXZrAWQejK2H3aqw5XnOoNIXcVYlLYNB54iSucmFFpMBzQ6T61yBADK-CyjpczvKhyNnRNe0D5vtLBDezOLRYIDd9TDcwp1WNydji0DycDFz4YbAG3wBQcQJoMbjfAAMuB8yWC8Ia-IQAAzAQAGwAzuxmPVK3msLhOrX+32G83253UTnIA7850i1FHLH+AAjKsc1QsShIYQYQ0ADx9IFIEBa0ieHOkAEEAHatgD2QwAOm2AJJXvj7r4ArebsTJeSXm8W3vJ8AHkAFcABd3xVSlBynOsIHPEAABEAEshlQiDWyfV8-heJ5-nkE01mcWZ5mMPggA noborder}}
+</WRAP>
+\\ \\
+When the signal is not referred to the ground, the following circuit based on an instrumentation amplifier can be used. \\
+In this case, the input signal is **differential**. Referred to the ground the input signal (here the difference of $5 ~\rm mV$) can have an offset voltage with regard to the ground. \\
+An example of this setup is the [[https://www.ti.com/lit/ds/symlink/ina351.pdf|INA 351]].
+<WRAP>{{url>https://www.falstad.com/circuit/circuitjs.html?running=false&ctz=CQAgjCAMB0l3BWcMBMcUHYMGZIA4UA2ATmIxAUgpABZsKBTAWjDACgAnEPKsPG7lTRVekMGPZceIFGEKCZ2FFBDFxkTgpQ08WwgNFi2AdwVgM86XwMmtcO7o2npaXS7lRbLpVpoivQn6+jgHgFuDy5vJODhEy+J6mHtpULkEaAG4gLMTKuAI5yvoqVOmwkEgiUNAIbHJUTMVgudk+zcoQMHAQ6vB9GvXZHoPDhLzV3cj9fXVjQ-Io2nGLAp3lPdMzpiyRc0xtczH7HXtt4UfJS8cyS0c+K63KrolxYDQCVu8vTFYtjastDRochMHQRXTXOS6AQAZXY2zBUOyiPOtl42Gi4C+QMg5HRu3AGNoIBhOLx8V4C3ssJiQnsdJCwOyLgQ8iYrJkHJpbAAMsyhD4WGAnvcVAAzACGABsAM4Mahk-mKZTshY+WHsABG2TUqnolBkWE8AA9sigELo5MQzQlzMpVsoAIIAO2lAHsAOYAHRlAElnWxTToILJrQgaCHFsThSAXe7vTKAPIAVwALoGhgbZBAWJABLIBA6QAARACWHtLqelPv9bAl4BQukbTYSze44CQLCQvXgE0gpAHA76NFIjlgG02dYbbgZCmtYE7C6mfQmb0Ho5HpE3Y7E3c2MWewstjenLyPp-PxGitnPmA6J5SZ4fQWej6OvxVVhjMS-n94395JVzTZVgng5ZQqElWV5UqKclF4Fo-AQ5RLUXPd+j7QdKDEPAcDwfRii6fsB2wlBsBwDA3iafdNHg2JpEMDQuDottXzwRxl00CMFnYkAWN4xiuI8aQ6IYzjTBYhJ+JCCS0DCeRRP8UxuIUFT2heNTEPsdSLhafIhhPfSUFsQoQGKFgT2KYyuGeFxbRPKhsPgTRXxfVsBIofpQjeD5-wgtgslM7AEBVdT9KqMoxBKapag9IY9JC+K8kIDiNFNJhtAEbBzDNMB6DootEzFMU5XTbZzyaSybHKwy81PcLQjvU8mpiS9LCoK8XmkTrfy6oQMBQoRCLYAAHWgmkQqzePoJTaGSXiaCmmS5siSaAX8oA noborder}}
+</WRAP>
 ====== Exercises ======