CN220022761U - Low-frequency logarithmic amplifier - Google Patents
Low-frequency logarithmic amplifier Download PDFInfo
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- CN220022761U CN220022761U CN202321588065.3U CN202321588065U CN220022761U CN 220022761 U CN220022761 U CN 220022761U CN 202321588065 U CN202321588065 U CN 202321588065U CN 220022761 U CN220022761 U CN 220022761U
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Abstract
The utility model relates to the technical field of amplifiers, in particular to a low-frequency logarithmic amplifier, which comprises a first reverse operational amplifier circuit and a second reverse operational amplifier circuit, wherein the first reverse operational amplifier circuit comprises a first resistor, a second resistor, a first operational amplifier, a first capacitor, a first transistor, a third resistor and a second transistor, the second reverse operational amplifier circuit comprises a fourth resistor, a second operational amplifier, a fifth resistor, a second capacitor, an eighth resistor, a ninth resistor in parallel connection, a seventh resistor and a sixth resistor, the logarithmic amplifier uses square wave signals to analyze the input, output and frequency characteristics, the analysis result shows that the smaller the gain of an output signal is, the larger the gain of the output signal is, the weak signal can be amplified, the amplitude of the output signal is reduced along with the increase of the amplitude of the input signal, the problem that the dynamic range of the input signal is large, and the conventional common logarithmic amplifier can not meet the requirements of the amplifier in the wide dynamic range field can be solved.
Description
Technical Field
The utility model relates to the technical field of amplifiers, in particular to a low-frequency logarithmic amplifier.
Background
A logarithmic amplifier is a signal amplifier for amplifying an effective value of a certain signal, and its signal gain is determined by a change of a logarithmic function thereof, thus having a large gain anti-interference performance.
Common logarithmic amplifiers can be classified into integrated circuit logarithmic amplifiers, demodulation logarithmic amplifiers, and half-wave gate-based logarithmic amplifiers. The logarithmic amplifier of the integrated circuit is also called an inverting amplifier, can respond to the input of change, has higher gain, can effectively improve the level and quality of signals, but has low reliability, and is easy to influence the precision of the signals due to the change of the ambient temperature; demodulation logarithmic amplifier is also called step-by-step detection logarithmic amplifier, which can obtain good logarithmic transfer characteristic, but tends to have larger power consumption, basically more than 30mA; the logarithmic amplifier based on the half-wave gate is also called a half-wave gate amplifier, has the advantages of realizing a large-range adjustable dynamic range, enabling output voltage to show logarithmic relation along with the change of input voltage, effectively solving the problem of static noise, and having the defect of small dynamic range.
The conventional logarithmic amplifier cannot meet the requirements of the logarithmic amplifier with high precision, low power consumption and high gain in the field of wide dynamic range of input signals.
Disclosure of Invention
The utility model aims to provide a low-frequency logarithmic amplifier and aims to solve the problem that the existing common logarithmic amplifier cannot meet the requirement of the amplifier in the field of wide dynamic range.
In order to achieve the above object, the present utility model provides a low frequency logarithmic amplifier, comprising a first inverting operational amplifier circuit and a second inverting operational amplifier circuit, wherein the first inverting operational amplifier circuit is electrically connected with the second inverting operational amplifier circuit;
the first reverse operational amplifier circuit comprises a first resistor, a second resistor, a first operational amplifier, a first capacitor, a first transistor, a third resistor and a second transistor, wherein the first resistor is connected with the negative end of the first operational amplifier, the second resistor is connected with the positive end of the first operational amplifier, the first transistor is connected in series with the first resistor, the third resistor is connected in series with the first transistor and the first operational amplifier, and the first capacitor is connected in parallel with the first transistor and the third resistor and is connected in series with the second transistor;
the second reverse operational amplifier circuit comprises a fourth resistor, a second operational amplifier, a fifth resistor, a second capacitor, an eighth resistor, a ninth resistor in parallel connection, a seventh resistor and a sixth resistor, wherein the second operational amplifier negative end is connected with the second transistor in series, the fifth resistor is connected with the second operational amplifier positive end in series, the second transistor is respectively connected with the eighth resistor and the seventh resistor in series, the ninth resistor is connected with the eighth resistor and the second operational amplifier in series, the sixth resistor is connected with the ninth resistor in series, and the second capacitor is connected with the eighth resistor, the seventh resistor and the ninth resistor in parallel connection.
Wherein the low frequency logarithmic amplifier reference voltage is 5V.
And one end of the second resistor far away from the first operational amplifier is grounded.
And one end of the fifth resistor far away from the second operational amplifier is grounded.
Wherein the first transistor and the second transistor are identical in special effect.
The utility model relates to a low-frequency logarithmic amplifier, which is characterized in that a first resistor is connected with the negative end of a first operational amplifier, a second resistor is connected with the positive end of the first operational amplifier, a first capacitor is connected with a first transistor and a third resistor in parallel and then connected with a second transistor in series, a fourth resistor is connected with the negative end of the second operational amplifier, the positive end of the second operational amplifier is connected with a fifth resistor, the second capacitor is connected with an eighth resistor and a ninth resistor in parallel, a seventh resistor is connected with the eighth resistor in series and connected with the ground, the output end of the second operational amplifier is connected with a sixth resistor, the logarithmic amplifier analyzes the input, output and frequency characteristics by square wave signals, and the result shows that when the input signal is lower than 10mA, the amplifier has good amplification characteristics, the dynamic range of the input signal reaches 50d, the maximum small signal gain can reach 70dB, the analysis result shows that the smaller the output signal is, the larger the gain is, the weak signal can be amplified, the amplitude of the output signal is reduced along with the increase of the amplitude of the input signal, the large dynamic range of the input signal can be solved, the output signal has high gain when the input signal is lower than 10mv, the gain of the output signal is reduced logarithmically along with the increase of the signal, the low-frequency logarithmic amplifier achieves 6V when the input signal is 3mv at low frequency, the smaller the small signal gain is 66dB, the larger the smaller the gain is, the weak signal can be amplified, the low-frequency amplifier has good consistency, the later stage is not required to be debugged, the large-scale production application is realized, and the problem that the existing common logarithmic amplifier cannot meet the requirement of the amplifier in the wide dynamic range field is solved.
Drawings
In order to more clearly illustrate the embodiments of the utility model or the technical solutions in the prior art, the drawings that are required in the embodiments or the description of the prior art will be briefly described, it being obvious that the drawings in the following description are only some embodiments of the utility model, and that other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
Fig. 1 is a schematic circuit diagram of a conventional low frequency logarithmic amplifier.
Fig. 2 is a schematic circuit diagram of a low-frequency logarithmic amplifier according to the present utility model.
Fig. 3 is a schematic diagram of input/output characteristics of a low frequency logarithmic amplifier according to the present utility model.
In the figure: 201-first resistor, 202-second resistor, 203-first operational amplifier, 204-first capacitor, 205-first transistor, 206-third resistor, 207-second transistor, 208-fourth resistor, 209-fifth resistor, 210-second operational amplifier, 211-second capacitor, 212-sixth resistor, 213-ninth resistor in parallel, 214-eighth resistor, 215-seventh resistor.
Detailed Description
Embodiments of the present utility model are described in detail below, examples of which are illustrated in the accompanying drawings, wherein like or similar reference numerals refer to like or similar elements or elements having like or similar functions throughout. The embodiments described below by referring to the drawings are illustrative and intended to explain the present utility model and should not be construed as limiting the utility model.
Referring to fig. 1 to 3, the present utility model provides a low-frequency logarithmic amplifier, which includes a first inverting operational amplifier circuit and a second inverting operational amplifier circuit, wherein the first inverting operational amplifier circuit is electrically connected with the second inverting operational amplifier circuit;
the first reverse operational amplifier circuit comprises a first resistor, a second resistor, a first operational amplifier, a first capacitor, a first transistor, a third resistor and a second transistor, wherein the first resistor is connected with the negative end of the first operational amplifier, the second resistor is connected with the positive end of the first operational amplifier, the first transistor is connected in series with the first resistor, the third resistor is connected in series with the first transistor and the first operational amplifier, and the first capacitor is connected in parallel with the first transistor and the third resistor and is connected in series with the second transistor;
the second reverse operational amplifier circuit comprises a fourth resistor, a second operational amplifier, a fifth resistor, a second capacitor, an eighth resistor, a ninth resistor in parallel connection, a seventh resistor and a sixth resistor, wherein the second operational amplifier negative end is connected with the second transistor in series, the fifth resistor is connected with the second operational amplifier positive end in series, the second transistor is respectively connected with the eighth resistor and the seventh resistor in series, the ninth resistor is connected with the eighth resistor and the second operational amplifier in series, the sixth resistor is connected with the ninth resistor in series, and the second capacitor is connected with the eighth resistor, the seventh resistor and the ninth resistor in parallel connection.
In this embodiment, the second transistor 207 and the first transistor 205 are constituted by two transistors having the same characteristics, which has the advantage that the influence of the reverse saturation current of the transistors can be eliminated. For the reverse op-amp circuit, "the second resistor 202" is grounded so that the voltage of the first op-amp 203 is approximately equal to 0, and therefore all small signal current flows through the first transistor 205.
When an input signal Ui is applied to the inverting input of the first inverting operational amplifier circuit from left to right as shown in fig. 1, the second resistor 202 inverting the positive terminal of the first operational amplifier 203 is grounded, thereby ensuring that the current flowing through the first resistor 201 substantially flows to the first transistor 205. A reference voltage Uref is added to the reverse end of the second operational amplifier 210, and the fifth resistor 209 inverting the positive end of the second operational amplifier 210 is grounded, so that the current of the fourth resistor 208 inverting the reverse input end of the second operational amplifier 210 is ensured to basically flow to the second transistor 207.
The input and output relationship of the low frequency logarithmic amplifier shown is:
wherein: ui is an input signal of the low-frequency logarithmic amplifier, the first resistor 201 is an input resistor of the first operational amplifier 203 of the low-frequency logarithmic amplifier, uref is a reference voltage, the low-frequency logarithmic amplifier sets a value of Uref to 5V, and the fourth resistor 208 is an input resistor at an opposite end of the second operational amplifier 210 of the low-frequency logarithmic amplifier; the second resistor 202 at the positive end of the second operational amplifier 210 of the low frequency logarithmic amplifier is grounded, so that the current I1 flowing through the first resistor 201 flows to the first transistor 205; the fifth resistor 209 at the positive end of the second operational amplifier 210 of the low frequency logarithmic amplifier is grounded, so that the current Iref flowing through the fourth resistor 208 flows to the second transistor 207; the eighth resistor 214, the ninth resistor 213, and the seventh resistor 215 of the low frequency logarithmic amplifier constitute an inverting operational amplifier; v (V) T The magnitude of the thermal voltages of the first transistor 205 and the second transistor 207 for the low frequency logarithmic amplifier varies with temperature.
When the resistance of the first resistor 201 and the fourth resistor 208 of the low-frequency logarithmic amplifier are consistent, the input-output relationship of the low-frequency logarithmic amplifier is:
the input and output of the low-frequency logarithmic amplifier obeys the logarithmic relation, the input and output characteristics of the low-frequency logarithmic amplifier are shown in fig. 3, an ideal curve is obtained by the input and output relation (4) of the low-frequency logarithmic amplifier at the frequency of 15HZ, and a fitting curve is obtained by fitting the input and output data of the low-frequency logarithmic amplifier at the frequency of 15 HZ. As can be seen from fig. 3, when the input signal of the low-frequency logarithmic amplifier is 3mv, the output signal reaches 6V, the small signal gain is 66dB, and the smaller the signal gain is, the larger the gain can be used for amplifying weak signals. The amplitude of the output signal of the low-frequency logarithmic amplifier shown in fig. 3 is reduced along with the increase of the amplitude of the input signal, so that the problem of large dynamic range of the input signal can be solved.
The above disclosure is merely illustrative of a preferred embodiment of the low frequency logarithmic amplifier of the present utility model, and it is not intended to limit the scope of the utility model.
Claims (5)
1. A low frequency logarithmic amplifier is characterized in that,
the high-voltage power supply circuit comprises a first reverse operational amplifier circuit and a second reverse operational amplifier circuit, wherein the first reverse operational amplifier circuit is electrically connected with the second reverse operational amplifier circuit;
the first reverse operational amplifier circuit comprises a first resistor, a second resistor, a first operational amplifier, a first capacitor, a first transistor, a third resistor and a second transistor, wherein the first resistor is connected with the negative end of the first operational amplifier, the second resistor is connected with the positive end of the first operational amplifier, the first transistor is connected in series with the first resistor, the third resistor is connected in series with the first transistor and the first operational amplifier, and the first capacitor is connected in parallel with the first transistor and the third resistor and is connected in series with the second transistor;
the second reverse operational amplifier circuit comprises a fourth resistor, a second operational amplifier, a fifth resistor, a second capacitor, an eighth resistor, a ninth resistor in parallel connection, a seventh resistor and a sixth resistor, wherein the second operational amplifier negative end is connected with the second transistor in series, the fifth resistor is connected with the second operational amplifier positive end in series, the second transistor is respectively connected with the eighth resistor and the seventh resistor in series, the ninth resistor is connected with the eighth resistor and the second operational amplifier in series, the sixth resistor is connected with the ninth resistor in series, and the second capacitor is connected with the eighth resistor, the seventh resistor and the ninth resistor in parallel connection.
2. A low frequency logarithmic amplifier according to claim 1, wherein,
the low frequency logarithmic amplifier reference voltage is 5V.
3. A low frequency logarithmic amplifier according to claim 1, wherein,
and one end of the second resistor far away from the first operational amplifier is grounded.
4. A low frequency logarithmic amplifier according to claim 1, wherein,
and one end of the fifth resistor far away from the second operational amplifier is grounded.
5. A low frequency logarithmic amplifier according to claim 1, wherein,
the first transistor and the second transistor are identical in special effect.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202321588065.3U CN220022761U (en) | 2023-06-21 | 2023-06-21 | Low-frequency logarithmic amplifier |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202321588065.3U CN220022761U (en) | 2023-06-21 | 2023-06-21 | Low-frequency logarithmic amplifier |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CN220022761U true CN220022761U (en) | 2023-11-14 |
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Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CN202321588065.3U Active CN220022761U (en) | 2023-06-21 | 2023-06-21 | Low-frequency logarithmic amplifier |
Country Status (1)
| Country | Link |
|---|---|
| CN (1) | CN220022761U (en) |
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2023
- 2023-06-21 CN CN202321588065.3U patent/CN220022761U/en active Active
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