An automatically adjustable attenuator circuit for radio frequencies

Abstract

This invention relates to an automatically adjustable radio frequency (RF) attenuation circuit. It includes a detector unit, an RF switch, and an attenuation unit. The detector unit outputs a control voltage based on the magnitude of the input RF signal, driving the RF switch and attenuation unit to automatically switch between multiple attenuation levels. The attenuation unit is constructed using a π-type resistor network and switching diodes, with input and output voltage standing wave ratios (VSWRs) both less than 1.3. This invention requires no external control and can automatically adjust the attenuation based on the input signal amplitude. It is suitable for high-frequency and small-signal scenarios and has the advantages of low cost and stable performance.

Description

Technical Field

[0001] This utility model relates to an automatically adjustable radio frequency attenuation circuit. Background Technology

[0002] In the field of radio frequency (RF), attenuation is often used to control the amplitude of transmitted or received signals. Since the magnitude of signals varies, attenuation circuits often need to achieve different attenuation levels. However, due to the high-frequency environment and the difficulty in detecting small signals, switching between different attenuation levels often relies on software and external control.

[0003] For example, existing technology: an adjustable RF attenuator (patent document 201320230330.0) has the following defects: 1. The attenuation unit relies on external control signals or control voltages and cannot achieve automatic adjustment; 2. It does not detect the input RF signal, and the attenuation amount is not related to the magnitude of the input RF signal; 3. It has few attenuation levels, with only attenuation and no attenuation; 4. The attenuator uses a single resistor in series, and its input-output VSWR is not good enough; 5. It uses more integrated components, resulting in higher cost.

[0004] In summary, existing RF attenuators mostly rely on external control signals or voltages, cannot achieve automatic adjustment, have limited attenuation levels, and exhibit poor VSWR performance. Furthermore, current technologies are costly and struggle to meet the needs of high-frequency and small-signal applications. Utility Model Content

[0005] In view of the problems existing in the prior art, the purpose of this utility model is to provide a technical solution for an automatically adjustable radio frequency attenuation circuit.

[0006] The automatically adjustable radio frequency attenuation circuit is characterized by comprising a detection unit, a radio frequency switch, and an attenuation unit.

[0007] The detection unit includes three detection circuits, namely the first detection unit, the second detection unit and the third detection unit, which are used to detect radio frequency signals of different amplitudes and output corresponding control voltages respectively;

[0008] The radio frequency switch includes a first switch and a second switch, which selects the path based on the received enable voltage;

[0009] The attenuation unit includes attenuation unit 1 and attenuation unit 2, which respectively achieve smaller and larger attenuation amounts, and each attenuation unit has two switchable levels;

[0010] After the radio frequency signal is input, it is connected to the first detection unit, the second detection unit, the third detection unit and the first switch respectively. The first detection unit is connected to the first switch and the second switch. The second detection unit is connected to the attenuation unit 2. The third detection unit is connected to the attenuation unit 1. The attenuation unit 1 and the attenuation unit 2 are connected to the first switch and the second switch respectively and are selected through the first switch and the second switch. The radio frequency signal is output from the second switch.

[0011] The first detector unit detects the signal, converts the AC signal into DC voltage, and then controls the first and second switches to select the path; the second detector unit detects the signal, converts the AC signal into DC voltage, and then controls the attenuation unit 2 to switch the attenuation amount; the third detector unit detects the signal, converts the AC signal into DC voltage, and then controls the attenuation unit 1 to switch the attenuation amount.

[0012] The parameters of the three detection units are different, and they will have different output voltages for different amplitude radio frequency signals. The two attenuation units in the later stage are controlled by voltage, thereby realizing automatic switching of attenuation according to the magnitude of the input radio frequency signal.

[0013] The automatically adjustable radio frequency attenuation circuit is characterized in that the detection circuit consists of a Schottky diode, a capacitor, and an operational amplifier, used to convert AC signals into DC control voltage.

[0014] The automatically adjustable radio frequency attenuation circuit is characterized in that the attenuation unit is composed of a π-type resistor network and a switching diode. The π-type resistor network changes the attenuation amount by switching the diode in the on or off state, thereby realizing the switching of multiple attenuation levels.

[0015] The automatically adjustable radio frequency attenuation circuit is characterized in that the attenuation amount of the attenuation unit can be switched in any combination according to the selection of the resistance value, and the input and output voltage standing wave ratios are both less than 1.3.

[0016] The automatically adjustable radio frequency attenuation circuit is characterized in that the radio frequency switch adopts the MXD8621C model, which switches the signal path according to the control voltage.

[0017] This invention's attenuation circuit requires no external control; the attenuation level is controlled by the detection unit based on the magnitude of the input RF signal. The circuit consists of a detection circuit, an RF switch, and an attenuation unit. The attenuation unit comprises a π-type resistor network and switching diodes, offering up to four attenuation levels. The attenuation level can be arbitrarily combined based on the selected resistor values, with both input and output voltage standing wave ratios (VSWRs) less than 1.3. The detection unit consists of Schottky diodes and operational amplifiers, suitable for high-frequency signals up to hundreds of megahertz and low-frequency signals with peak values ​​as low as a few tenths of a volt. The entire circuit, composed of resistors, capacitors, diodes, and operational amplifiers, is inexpensive, costing no more than 10 yuan. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the first detector unit;

[0019] Figure 2 This is a schematic diagram of the second detector unit;

[0020] Figure 3 This is a schematic diagram of the third detector unit;

[0021] Figure 4 This is a schematic diagram of attenuation unit 1;

[0022] Figure 5 This is a schematic diagram of attenuation unit 2;

[0023] Figure 6 This is a schematic diagram illustrating the working principle of this utility model;

[0024] Figure 7 This is the circuit diagram of this utility model;

[0025] Figure 8 This is a circuit block diagram of the present invention. Detailed Implementation

[0026] The present invention will be further described below with reference to the accompanying drawings:

[0027] An automatically adjustable radio frequency attenuation circuit consists of a detector unit, a radio frequency switch, and an attenuation unit.

[0028] The detection unit includes three detection circuits, namely the first detection unit, the second detection unit and the third detection unit, which are used to detect radio frequency signals of different amplitudes and output corresponding control voltages.

[0029] The radio frequency switch includes a first switch and a second switch, which selects the path based on the received enable voltage.

[0030] The attenuation unit includes attenuation unit 1 and attenuation unit 2, which respectively achieve smaller and larger attenuation amounts, and each attenuation unit has two switchable levels.

[0031] After the radio frequency signal is input, it is connected to the first detection unit, the second detection unit, the third detection unit and the first switch respectively. The first detection unit is connected to the first switch and the second switch. The second detection unit is connected to the attenuation unit 2. The third detection unit is connected to the attenuation unit 1. The attenuation unit 1 and the attenuation unit 2 are connected to the first switch and the second switch respectively and are selected through the first switch and the second switch. The radio frequency signal is output from the second switch.

[0032] The first detector unit detects the signal, converts the AC signal into DC voltage, and then controls the first and second switches to select the path; the second detector unit detects the signal, converts the AC signal into DC voltage, and then controls the attenuation unit 2 to switch the attenuation amount; the third detector unit detects the signal, converts the AC signal into DC voltage, and then controls the attenuation unit 1 to switch the attenuation amount.

[0033] The parameters of the three detection units are different, and they will have different output voltages for different amplitude radio frequency signals. The two attenuation units in the later stage are controlled by voltage, thereby realizing automatic switching of attenuation according to the magnitude of the input radio frequency signal.

[0034] Specifically, the detection circuit consists of Schottky diodes, capacitors, and operational amplifiers, used to convert AC signals into DC control voltages; the attenuation unit consists of a π-type resistor network and switching diodes. The π-type resistor network changes the attenuation by switching the diodes on or off, enabling switching between multiple attenuation levels. The attenuation of the attenuation unit can be switched in any combination based on the selected resistor values, and the input and output voltage standing wave ratios are both less than 1.3; the RF switch uses the MXD8621C model, which switches the signal path according to the control voltage; the operational amplifiers Q1, Q2, and Q3 are model 3554AM.

[0035] The circuit structure of the first detection unit is as follows: Figure 1 As shown, a Schottky diode D1 is used to detect the peak of the radio frequency signal, and capacitor C1 discharges and stabilizes the voltage when the AC signal is in the negative half-axis. Then, the signal is amplified by a non-inverting operational amplifier, and the output control voltage V1 is generated. The values ​​of resistors R2 and R3 determine the amplification factor.

[0036] The circuit structure of the second detection unit is as follows: Figure 2 As shown, a Schottky diode D2 is used to detect high-intensity radio frequency signals. The capacitor C2 discharges and stabilizes the signal when it is on the negative half-axis of the AC signal. The signal is then amplified by a non-inverting operational amplifier, which outputs a control voltage V1. The values ​​of resistors R19 and R17 determine the amplification factor.

[0037] The circuit structure of the third detection unit is as follows: Figure 3As shown, a Schottky diode D3 is used to detect low-intensity radio frequency signals. The Schottky diode D3 performs peak detection on the radio frequency signal, and the capacitor C8 discharges and stabilizes the voltage when the AC signal is in the negative half-axis. When the signal is very small, the Schottky diode D3 outputs a negative voltage, which is then amplified by an inverting operational amplifier, outputting a positive control voltage V3. The values ​​of resistors R23 and R12 determine the amplification factor.

[0038] The circuit structure of attenuation unit 1 is as follows Figure 4 As shown: π-type network. When the switching diodes D4 and D5 are in the off state, the resistors R14 and R15 are equivalent to disconnecting the circuit, and the signal passes through directly without attenuation. When the switching diodes D4 and D5 are in the on state, the resistors R14 and R15 are grounded to achieve attenuation, and the capacitors C4 and C7 are used to block DC.

[0039] The circuit structure of attenuation unit 2 is as follows Figure 5 As shown: π-type network. When the switching diodes D6 and D7 are in the off state, the resistors R24 and R25 are disconnected from the circuit, and the attenuation is formed by the resistors R6, R7 and R8. When the switching diodes D6 and D7 are in the on state, the resistors R24 and R25 are connected to the circuit, the equivalent resistance to ground decreases, and the attenuation increases. The capacitors C11 and C12 are used to block DC.

[0040] Attenuation unit 1: Smaller attenuation, capable of two attenuation levels; Attenuation unit 2: Larger attenuation, capable of two attenuation levels.

[0041] The first and second switches use the MXD8621C model. VDD is the power supply pin, ANT is the input / output pin, VC is the enable pin, and RF1 and RF2 are the channel selection pins. When VC is high, the channel selection is RF2; when VC is low, the channel switches to RF2. This circuit connects the RF1 pins of the two switches, connects the RF2 pins of the two switches, and connects the VC pins of both switches to the control voltage V1, thereby achieving the switching of the switch channels.

[0042] The specific circuit connection is as follows:

[0043] After the RF signal is input, it is connected to pin 5 of the first, second, and third detector units and the first switch via resistor R29. The circuit structures of the first, second, and third detector units are the same, but the component parameters are different, as follows: After the RF signal is input, it is connected to resistor R27 via resistor R29. Resistor R27 is connected to one end of resistor R1 and one end of capacitor C1 via Schottky diode D1. The other end of capacitor C1 is grounded. The other end of resistor R1 is connected to pin 1 of operational amplifier Q1. Operational amplifier Q... Pin 5 of switch 1 is connected to VCC3V3 and one end of capacitor C17. The other end of C17 is grounded. Pin 2 of operational amplifier Q1 is grounded. Pin 3 of operational amplifier Q1 is connected to one end of resistor R2 and one end of resistor R3. The other end of resistor R2 is grounded. The other end of resistor R3 is connected to pin 4 of operational amplifier Q1 and one end of resistor R26. The other end of resistor R26 is connected to one end of capacitor C14 and one end of resistor R28. The other end of capacitor C14 is grounded. The other end of resistor R28 is connected to pin 6 of the first switch U1 and pin 6 of the second switch U2.

[0044] After the RF signal is input, it is connected to resistor R20 via resistor R29. Resistor R20 is connected to one end of resistor R21 and one end of capacitor C2 via Schottky diode D2. The other end of capacitor C2 is grounded. The other end of resistor R21 is connected to pin 1 of operational amplifier Q2. Pin 5 of operational amplifier Q2 is connected to VCC3V3 and one end of capacitor C16. The other end of capacitor C16 is grounded. Pin 2 of operational amplifier Q2 is grounded. Pin 3 of operational amplifier Q2 is connected to one end of resistor R19 and one end of resistor R17. The other end of resistor R19 is grounded. The other end of resistor R17 is connected to pin 4 of operational amplifier Q2 and one end of resistor R18. The other end of resistor R18 is connected to one end of capacitor C9 and one end of resistor R22. The other end of capacitor C9 is grounded. The other end of resistor R22 is connected to one end of capacitor C13, the anode of diode D6, and the anode of diode D7. The other end of capacitor C13 is grounded.

[0045] After the RF signal is input, it is connected to pin 5 of the first switch U1 via resistor R29. Pin 4 of the first switch U1 is connected to one end of capacitor C3 and one end of resistor R4. The other end of capacitor C3 is grounded, and the other end of resistor R4 is connected to VCC3V3. Pin 2 of the first switch U1 is grounded. Pin 3 of the first switch U1 is connected to one end of capacitor C4. Pin 1 of the first switch U1 is connected to one end of capacitor C11. The other end of capacitor C11 is connected to one end of resistor R24, one end of resistor R6, and one end of resistor R7. The other end of resistor R24 ​​is connected to the cathode of diode D6, and the other end of resistor R7... One end of the resistor is grounded. The other end of the resistor R6 is connected to one end of the resistor R8, one end of the resistor R25, and one end of the capacitor C12. The other end of the resistor R8 is grounded. The other end of the resistor R25 is connected to the negative terminal of the diode D7. The other end of the capacitor C12 is connected to pin 1 of the second switch U2. Pin 2 of the second switch U2 is grounded. Pin 3 of the second switch U2 is connected to one end of the capacitor C7. Pin 5 of the second switch U2 is the RF signal output terminal. Pin 4 of the second switch U2 is connected to one end of the capacitor C5 and one end of the resistor R5. The other end of the resistor R5 is connected to VCC3V3. The other end of the capacitor C5 is grounded.

[0046] After the RF signal is input, it is connected to resistor R13 via resistor R29. Resistor R13 is connected to one end of resistor R9 via Schottky diode D3. The other end of resistor R9 is connected to one end of resistor R23 and one end of capacitor C8. The other end of capacitor C8 is grounded. The other end of resistor R23 is connected to pin 3 of operational amplifier Q3. Pin 1 of operational amplifier Q3 is grounded. Pin 5 of operational amplifier Q3 is connected to VCC3V3 and one end of capacitor C15. The other end of capacitor C15 is grounded. Pin 2 of operational amplifier Q3 is grounded. Pin 3 of operational amplifier Q3 is connected to one end of resistor R12. Resistor R1... 2. Connect the other end to pin 4 of operational amplifier Q3 and one end of resistor R10. Connect the other end of resistor R10 to one end of capacitor C10 and one end of resistor R11. Connect the other end of capacitor C10 to ground. Connect the other end of resistor R11 to one end of capacitor C6, the positive terminal of diode D4, and the positive terminal of diode D5. Connect the other end of capacitor C6 to ground. Connect the negative terminal of diode D4 to one end of resistor R14. Connect the other end of resistor R14 to one end of capacitor C4 and one end of resistor R16. Connect the negative terminal of diode D5 to one end of resistor R15. Connect the other end of resistor R15 to one end of resistor R16 and one end of capacitor C7.

[0047] The circuit operation of this utility model is as follows:

[0048] The priority of the three detection circuits is as follows: the output V1 of the first detection circuit is connected to the enable control pin of the first and second switches to switch attenuation unit 1 and attenuation unit 2. The other two detection circuits select the attenuation amount under this premise; the output V2 of the second detection circuit only affects attenuation unit 2; the output V3 of the third detection circuit only affects attenuation unit 1.

[0049] The radio frequency (RF) signal is set with three threshold values, S1, S2, and S3 from largest to smallest (the detection signal threshold is mainly determined by the voltage regulator capacitor to ground and the amplification factor). Three detection units detect the signal in real time and output control voltages. The output voltage of the first detection unit is V1, the output voltage of the second detection unit is V2, and the output voltage of the third detection unit is V3. The states of these three control voltages are represented by 1 and 0. 1 indicates that the voltage has reached the threshold value and can drive the RF switch or turn on the switching diode; 0 indicates that the voltage is insufficient and cannot drive the RF switch or turn off the switching diode. Attenuation can be achieved in four levels, from smallest to largest, denoted as A, B, C, and D. The control logic is as follows: When the amplitude of the input RF signal is greater than S1, V1 and V2 output 1. At this time, the control voltage drives the V1 RF switch to switch the path to attenuation unit 2, and the control voltage V2 turns on diodes D6 and D7, with the attenuation level being the maximum attenuation level D. When the amplitude of the RF signal is between S1 and S2, V1 outputs 1, V2 outputs 0, the control voltage V1 drives the RF switch to switch the path to attenuation unit 2, diodes D6 and D7 are turned off, and the attenuation level is C. When the amplitude of the RF signal is between S2 and S3, V1 outputs 0, V3 outputs 1, and the RF switch switches the path to... Attenuation unit 1, control voltage V3 turns on D4 and D5, attenuation level C; when the RF signal strength is less than S3, V1 output is 0, V3 output is 0, the RF switch switches the path to attenuation unit 1, diodes D4 and D5 are cut off, attenuation level A (the detector circuit is a circuit that converts RF signal to DC voltage, V1, V2, V3 equal to 0 or 1 is just for convenience in describing the state, V1>1.8V is 1, less than is 0; V2 and V3>0.7V is 1, less than is 0; V1, V2, V3 output 1 or 0 according to the input signal strength, the parameters or connection of the three detector circuits are different).

Claims

1. An automatically adjustable attenuator circuit for radio frequencies, characterized in that It consists of a detector unit, an RF switch, and an attenuation unit. The detection unit includes three detection circuits, namely the first detection unit, the second detection unit and the third detection unit, which are used to detect radio frequency signals of different amplitudes and output corresponding control voltages respectively; The radio frequency switch includes a first switch and a second switch, which selects the path based on the received enable voltage; The attenuation unit includes attenuation unit 1 and attenuation unit 2, which respectively achieve smaller and larger attenuation amounts, and each attenuation unit has two switchable levels; After the radio frequency signal is input, it is connected to the first detection unit, the second detection unit, the third detection unit and the first switch respectively. The first detection unit is connected to the first switch and the second switch. The second detection unit is connected to the attenuation unit 2. The third detection unit is connected to the attenuation unit 1. The attenuation unit 1 and the attenuation unit 2 are connected to the first switch and the second switch respectively and are selected through the first switch and the second switch. The radio frequency signal is output from the second switch. The first detector unit detects the signal, converts the AC signal into DC voltage, and then controls the first and second switches to select the path; the second detector unit detects the signal, converts the AC signal into DC voltage, and then controls the attenuation unit 2 to switch the attenuation amount; the third detector unit detects the signal, converts the AC signal into DC voltage, and then controls the attenuation unit 1 to switch the attenuation amount. The parameters of the three detection units are different, and they will have different output voltages for different amplitude radio frequency signals. The two attenuation units in the later stage are controlled by voltage, thereby realizing automatic switching of attenuation according to the magnitude of the input radio frequency signal.

2. An automatically adjustable attenuator circuit for radio frequencies as recited in claim 1, wherein The detection circuit consists of a Schottky diode, a capacitor, and an operational amplifier, and is used to convert AC signals into DC control voltage.

3. The automatically adjustable radio frequency attenuation circuit according to claim 1, characterized in that... The attenuation unit consists of a π-type resistor network and a switching diode. The π-type resistor network changes the attenuation amount by switching the diode in either the on or off state, thereby enabling switching between multiple attenuation levels.

4. The automatically adjustable radio frequency attenuation circuit according to claim 3, characterized in that... The attenuation of the attenuation unit can be switched in any combination according to the selection of the resistance value, and the input and output voltage standing wave ratios are both less than 1.

3.

5. The automatically adjustable radio frequency attenuation circuit according to claim 1, characterized in that... The radio frequency switch is model MXD8621C, which switches the signal path according to the control voltage.

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