CN107579732B - Analog switch circuit based on radio frequency switch chip - Google Patents
Analog switch circuit based on radio frequency switch chip Download PDFInfo
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- CN107579732B CN107579732B CN201710854449.8A CN201710854449A CN107579732B CN 107579732 B CN107579732 B CN 107579732B CN 201710854449 A CN201710854449 A CN 201710854449A CN 107579732 B CN107579732 B CN 107579732B
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Abstract
The invention discloses an analog switch circuit based on a radio frequency switch chip, which comprises the radio frequency switch chip, a linear voltage stabilizing module, an operational amplifier module and an optical coupler module; the radio frequency switch chip is respectively connected with the linear voltage stabilizing module, the operational amplifier module and the optocoupler module. The common output end of the radio frequency switch chip is connected to the low-pass filter, direct current components in signals are directly fed back to the radio frequency switch chip and the linear voltage stabilizer through the action of the operational amplifier, so that the voltage of the grounding end is changed along with the change of direct current voltage, and the power output end of the linear voltage stabilizer is also changed along with the change of voltage, thereby ensuring that the voltage difference between the power output end and the reference ground is a fixed value, realizing that no direct current voltage difference exists between the common output end of the radio frequency switch chip and the grounding end, meeting the condition that the direct current bias is zero, obviously improving the stability and the reliability of the radio frequency switch chip, and obtaining better switching characteristics. The invention also has the advantages of simple structure, low manufacturing cost and small volume.
Description
Technical Field
The invention relates to the field of analog switches, in particular to an analog switch circuit based on a radio frequency switch chip, wherein the switch frequency of the analog switch circuit is from direct current (0 Hz) to 4G (4 GHz).
Background
The existing switches comprise a reed relay, a photoelectric relay, a radio frequency switch, an MEMS switch and the like. The optical relay can pass through a direct current signal, but has poor high-frequency performance due to the influence of the mechanical structure. The general reed relay has better high-frequency performance than the optical relay, but is also within 1G. Some rf relays have high frequency characteristics, but are bulky and expensive. MEMS switches are small but also very expensive. The rf switch is inexpensive and small, and its frequency band can be infinitely close to DC, but due to its internal structure limitations, the signal must pass through a blocking capacitor or keep the DC level at 0.
Accordingly, there is a need in the art for further improvements and perfection.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provides an analog switch circuit based on a radio frequency switch chip, which can pass direct current.
The aim of the invention is achieved by the following technical scheme:
the analog switch circuit based on the radio frequency switch chip is an application circuit of the radio frequency switch chip, and is mainly used for solving the problem that the radio frequency switch chip cannot bear direct current level and realizing the control of the switching frequency from direct current (0 Hz) to 4 GHz. The radio frequency switch chip is respectively connected with the linear voltage stabilizing module, the operational amplifier module and the optocoupler module, and the circuit design can extract and feed back the direct current component of the common output end signal to the adjusting end of the linear voltage stabilizing module and the grounding end of the radio frequency switch chip, so that the output voltage of the linear voltage stabilizing module changes along with the direct current voltage, a voltage with a fixed voltage difference (3V) relative to the direct current voltage is provided for the radio frequency switch chip, the fact that no direct current voltage difference exists between the common output end and the grounding end of the radio frequency switch chip is finally achieved, and the condition that the direct current bias is zero is guaranteed, and therefore the static working point of the radio frequency switch chip cannot change along with the change of the input signal.
Specifically, the operational amplifier module comprises an operational amplifier and a low-pass filter for extracting a direct current component of an output signal. The low pass filter includes a first resistor for attenuating the high frequency signal and a first capacitor for filtering the high frequency signal. One end of the first resistor is connected with the public output end of the radio frequency switch chip, the other end of the first resistor is respectively connected with the positive input end of the operational amplifier and one end of the first capacitor, and the other end of the first capacitor is connected with power ground. And the positive and negative power supply input ends of the operational amplifier are respectively connected with the positive and negative power supplies. The reverse input end of the operational amplifier is respectively connected with the output end and the grounding end of the radio frequency switch chip, and the grounding end forms the reference ground (the voltage of the reference ground changes along with the voltage change of the forward input end), so that the voltage of the grounding end of the radio frequency switch chip changes along with the direct current voltage change of the common output end. The operational amplifier module circuit is actually a voltage follower circuit, and the effect of the operational amplifier is analyzed according to the principles of virtual short and virtual break, so that the voltage of a forward input end is the same as the voltage of a reverse input end, the voltage of an output end, the voltage of a grounding end of a radio frequency switch chip and the voltage of a reference ground, the voltage can change along with the voltage change of the output end of a low-pass filter, and the DC component of a signal of a common output end is extracted due to the effect of the low-pass filter, and is directly fed back to the grounding end of the radio frequency switch chip after passing through the voltage follower circuit, so that no DC pressure difference exists between the grounding end and the common output end, and the condition that the DC bias of the radio frequency switch chip is zero is ensured.
Specifically, the optocoupler module comprises an optocoupler and a second resistor, wherein the optocoupler is used for driving the radio frequency switch chip. The optical coupler is a common optical coupler, namely, the internal structure of the input end is an equivalent light-emitting diode, and the internal structure of the output end is equivalent a triode. The input end of the optical coupler is respectively connected with the control signal input end and the power ground, specifically, the control pin of the control chip is connected with the positive input end of the optical coupler, and the negative input end of the optical coupler is connected with the power ground. The output end of the optical coupler is respectively connected with the control end and the grounding end of the radio frequency switch chip, specifically, the collector electrode of the optical coupler is connected with the control end of the radio frequency switch chip, and the emitter electrode is connected with the grounding end. One end of the second resistor is connected with the power input end of the radio frequency switch chip, and the other end of the second resistor is connected with the control end. Because the voltage of the grounding end of the radio frequency switch chip changes along with the direct current voltage of the public output end, and the control chip for controlling the radio frequency switch chip and the radio frequency switch chip adopt different power supplies and grounds (namely, the voltage system of the input end of the optical coupler is different from the voltage system of the output end), in order to enable the radio frequency switch chip to be driven normally, the optical coupler is arranged between the control chip and the radio frequency switch chip as a driving module, so that the input end and the output end of the optical coupler are effectively isolated, and the normal operation of the radio frequency switch chip can be driven under the condition that the voltage systems of the input end and the output end are not changed is ensured, so that the stability and the reliability of chip driving are obviously improved.
Specifically, the linear voltage stabilizing module comprises a linear voltage stabilizer, a third resistor, a fourth resistor and a second capacitor. The power input end of the linear voltage stabilizer is connected with a first power supply. The power output end of the linear voltage stabilizer is respectively connected with the power input end of the radio frequency switch chip and one end of the fourth resistor, and forms a second power supply for supplying power. The other end of the fourth resistor is connected with the adjusting end of the linear voltage stabilizer and one end of the third resistor respectively, and the other end of the third resistor is connected with one end of the second capacitor and the reference ground respectively. The other end of the second capacitor is connected with the power ground, namely the reference ground is connected with the power ground through the second capacitor, the second capacitor is arranged by adopting a high-frequency capacitor and is mainly used for referencing the high-frequency signal on the ground, when the high-frequency signal passes through the reference ground, the impedance of the reference ground is ensured not to be suddenly changed, and the stability and the reliability of the switch system are effectively improved. Because the adjusting end of the linear voltage stabilizer is connected with the output end of the operational amplifier through the third resistor, when the direct current voltage of the common output end of the radio frequency switch chip changes to cause the voltage change of the output end of the operational amplifier, the voltage difference between the power output end of the linear voltage stabilizer and the adjusting end is a fixed value, so that the power output end of the linear voltage stabilizer can change along with the change of the reference ground voltage, the voltage difference between the power input end of the radio frequency switch chip and the ground end is unchanged, thereby reducing the fluctuation of the power supply voltage of the radio frequency switch chip and obviously improving the stability and the reliability of the power supply part.
Specifically, the first signal input end and the second signal input end of the radio frequency switch chip are respectively connected with the external signal input end, and the common output end is connected with the external equipment signal input end, so that the first signal input end is communicated with the common output end, or the second signal input end is communicated with the common output end.
Furthermore, in order to reduce the ac ripple coefficient at the output end of the linear voltage stabilizing module and smooth the dc voltage output, the linear voltage stabilizing module of the present invention further includes a third capacitor for improving the stability of the output voltage of the linear voltage stabilizer. One end of the third capacitor is connected with the power output end of the linear voltage stabilizer, and the other end of the third capacitor is connected with power ground. The purpose of the design is to filter out the high-frequency spike at the output end of the linear voltage stabilizer power supply by utilizing the filter characteristic of the third capacitor so as to stabilize the level of the direct current power supply.
In order to improve the universality of the circuit module, the first power supply adopts the power supply with the voltage of 10V, the voltage value is common voltage, the first power supply is suitable for various application circuits, the value of the voltage value is favorable for improving and reforming an old circuit, the reforming difficulty is reduced, the time is saved, and the reforming efficiency can be effectively improved.
As a preferred scheme of the invention, in order to improve the universality of a circuit module, the positive and negative power input ends of the operational amplifier are respectively connected with the power supplies of +5V and-5V power supplies, the voltage value is common voltage, the operational amplifier is suitable for various application circuits, the value of the voltage value is favorable for improving and reforming an old circuit, the reforming difficulty is reduced, the time is saved, and the reforming efficiency can be effectively improved.
As a preferable scheme of the invention, in order to meet the frequency change of the switch from zero hertz to 4 Ghertz, the radio frequency switch chip adopts a PE4245 radio frequency switch chip; in order to obtain a better switching effect, the operational amplifier disclosed by the invention adopts an OPA172 type operational amplifier with good direct-current stability and good temperature drift performance; the linear voltage stabilizer provided by the invention adopts the LM1117 linear voltage stabilizer with good power stability, high precision and high efficiency.
As a preferred solution of the present invention, since the linear voltage regulator with model LM1117 is adopted in the present invention, the voltage difference between the power output terminal and the regulation terminal of the linear voltage regulator is fixed to be 1.25V, in order to fix the voltage difference between the power output terminal and the reference ground of the linear voltage regulator to be 3V, the resistance ratio of the third resistor to the fourth resistor is adjusted to be 1.4, and the deduction principle and process thereof are as follows:
V out ＝V_GND+(R 3 +R 4 )*I R4 equation 1
The method can be obtained according to the formula 1: v (V) out ＝V_GND+(R 3 +R 4 )*(V out -V adj )/R 4 Equation 2
Wherein: v (V) out For the voltage of the power supply output terminal, V adj To adjust the terminal voltage, V_GND is the reference ground voltage, R 3 R is a third resistance 4 For the fourth resistance, I R4 For the current flowing through the fourth resistor, since Vout-Vadj is a fixed value of 1.25V, the order of substitution into equation 2 is obtained:
V out -V_GND＝1.25*(1+R 3 /R 4 ) Equation 3
Since V is required to be maintained in the above out The value of V_GND is 3V, so R is obtained by substitution into the post-finishing 3 /R 4 =1.4, i.e. the ratio of the resistance values of the third resistance to the fourth resistance is 1.4.
The working process and principle of the invention are as follows: the common output end of the radio frequency switch chip provided by the invention is connected to the low-pass filter, the direct current component in the signal is directly fed back to the grounding end of the radio frequency switch chip and the adjusting end of the linear voltage stabilizer through the voltage following action of the operational amplifier, so that the voltage of the grounding end becomes reference ground and changes along with the change of the direct current voltage, the power output end of the linear voltage stabilizer also changes along with the change of the voltage of the adjusting end, the voltage difference between the power output end and the reference ground is ensured to be a fixed value, the condition that the direct current voltage difference does not exist between the common output end and the grounding end of the radio frequency switch chip accords with the condition that the direct current bias is zero is realized, and therefore, the processing capacity, the stability and the reliability of the radio frequency switch chip are remarkably improved, and better switch characteristics are obtained; in addition, because different voltage systems are adopted between the radio frequency switch chip and the control chip, normal driving is realized through the optocoupler module, the stability and the reliability of a driving part can be improved through the design, and the two voltage systems can be effectively isolated, so that the interference between the two voltage systems is reduced, and the stability and the reliability of the system are effectively improved. The invention also has the advantages of simple structure, low manufacturing cost and small volume.
Compared with the prior art, the invention has the following advantages:
(1) The analog switch circuit based on the radio frequency switch chip provided by the invention combines the voltage following characteristic of the operational amplifier and the voltage automatic adjustment characteristic of the linear voltage stabilizer to supply power to the radio frequency switch chip, so that no direct current differential pressure exists between the common output end and the grounding end of the radio frequency switch chip, the condition that the direct current bias is zero is met, the problem that the direct current level cannot be borne is solved, and the real DC-4G electronic switch is realized.
(2) The analog switch circuit based on the radio frequency switch chip provided by the invention adopts the third capacitor to filter the power output end of the linear voltage stabilizer, so that the influence of high-frequency spike is filtered, the level of the direct-current power supply is stabilized, the radio frequency switch chip obtains stable power supply, and the stability and the reliability of the switch chip are ensured.
(3) The analog switch circuit based on the radio frequency switch chip provided by the invention adopts the optocoupler to drive the radio frequency switch chip, so that two sets of power supply systems with different voltages are compatible, isolated, normal driving of the radio frequency switch chip can be realized, and the stability and reliability of a driving part are improved.
Drawings
Fig. 1 is a schematic diagram of an analog switch circuit based on a radio frequency switch chip according to the present invention.
The reference numerals in the above figures illustrate:
the circuit comprises a U1-radio frequency switch chip, a U2-operational amplifier, a U3-linear voltage stabilizer, a U4-optical coupler, an R1-first resistor, an R2-second resistor, an R3-third resistor, an R4-fourth resistor, a C1-first capacitor, a C2-second capacitor and a C3-third capacitor;
VCC-first power supply, VDD-second power supply, V_GND-ground, RF 1-first signal input, RF 2-second signal input, RF-COM-common output.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more clear and clear, the present invention will be further described below with reference to the accompanying drawings and examples.
Example 1:
in the embodiment, a radio frequency switch PE4245 chip is used as a core, and a responsive driving circuit is matched to realize the electronic switch with the DC-4 GHz frequency.
PE4245 is a radio frequency switch of Peregrine Semiconductor company, adopts the GaAs technology of trap, and the bandwidth can reach 4G, but because of the limitation of technology and structure, the input port cannot have direct current level (which is clearly described in handbook), and all radio frequency ports must be added with blocking capacitance or ensure that the direct current level is zero. This results in that it cannot have an excessive direct current component, although the bandwidth can be from DC-4G. This is not just the case for a PE4245 chip, which is a problem for all GaAs chips.
In order to solve this problem, the bootstrap boost method is skillfully applied to enable the GND of the PE4245 to be consistent with the dc component of the RF-COM output signal of the common output terminal of the radio frequency chip instead of being connected to the actual GND (power ground). Thus, for the radio frequency port, no direct current voltage difference exists between the radio frequency port and the GND, and the condition that the direct current bias is zero is ensured. This allows the static operating point of the radio frequency switch to be unchanged with input signal, similar to the most basic JFET switch: the direct current component of the signal is extracted by adopting a low-pass filter and an operational amplifier, and then a 3V differential voltage source is formed by a single-ended differential circuit to supply power to the PE4245, and meanwhile, the GND of the PE4245 is connected with the power ground through a high-frequency capacitor, so that the impedance of the high-frequency signal is ensured not to be suddenly changed when the high-frequency signal passes through.
As shown in fig. 1, the invention discloses an analog switch circuit based on a radio frequency switch chip, which is an application circuit of the radio frequency switch chip U1, and is mainly used for solving the problem that the radio frequency switch chip U1 cannot bear a direct current level and realizing the control of a switching frequency from direct current (0 hz) to 4 ghz. The radio frequency switch chip U1 is respectively connected with the linear voltage stabilizing module, the operational amplifier module and the optocoupler module, and the circuit design can extract and feed back the direct current component of the common output end RF-COM signal to the adjusting end of the linear voltage stabilizing module and the grounding end of the radio frequency switch chip U1, so that the output voltage of the linear voltage stabilizing module changes along with the direct current voltage, a voltage with a fixed differential pressure (3V) relative to the direct current voltage is provided for the radio frequency switch chip U1, the fact that no direct current differential pressure exists between the common output end RF-COM of the radio frequency switch chip U1 and the grounding end, and the condition that the direct current bias is zero is guaranteed is achieved, and therefore the static working point of the radio frequency switch chip U1 cannot change along with the change of the input signal.
Specifically, the operational amplifier module comprises an operational amplifier U2 and a low-pass filter for extracting the direct current component of the output signal. The low-pass filter comprises a first resistor R1 for attenuating high-frequency signals and a first capacitor C1 for filtering out high-frequency signals. One end of the first resistor R1 is connected with the common output end RF-COM of the radio frequency switch chip U1, the other end of the first resistor R1 is respectively connected with the positive input end of the operational amplifier U2 and one end of the first capacitor C1, and the other end of the first capacitor C1 is connected with power ground. The positive and negative power supply input ends of the operational amplifier U2 are respectively connected with the positive and negative power supplies. The reverse input end of the operational amplifier U2 is respectively connected with the output end and the grounding end of the radio frequency switch chip U1, and the grounding end forms a reference ground V_GND (the voltage of the reference ground V_GND changes along with the voltage change of the forward input end), so that the voltage of the grounding end of the radio frequency switch chip U1 changes along with the direct current voltage change of the common output end RF-COM. The operational amplifier module circuit is actually a voltage follower circuit, and the effect of the operational amplifier U2 is analyzed according to the principles of virtual short and virtual break, so that the voltage of a forward input end is the same as the voltage of a reverse input end, the voltage of an output end, the voltage of a grounding end of the radio frequency switch chip U1 and the voltage of a reference ground V_GND, the voltage can be changed along with the voltage change of the output end of the low-pass filter, and the DC component of a public output end RF-COM signal is extracted due to the effect of the low-pass filter, so that the DC component is directly fed back to the grounding end of the radio frequency switch chip U1 after passing through the voltage follower circuit, no DC pressure difference exists between the grounding end and the public output end RF-COM, and the condition that the DC bias of the radio frequency switch chip U1 is zero is ensured.
Specifically, the optocoupler module includes an optocoupler U4 and a second resistor R2 for driving the radio frequency switch chip U1. The optical coupler U4 is a commonly used optical coupler U4, namely, the internal structure of the input end is an equivalent light emitting diode, and the internal structure of the output end is equivalent a triode. The input end of the optical coupler U4 is respectively connected with the control signal input end and the power ground, specifically, the control pin of the control chip is connected with the positive input end of the optical coupler U4, and the negative input end of the optical coupler U4 is connected with the power ground. The output end of the optical coupler U4 is respectively connected with the control end and the grounding end of the radio frequency switch chip U1, specifically, the collector of the optical coupler U4 is connected with the control end of the radio frequency switch chip U1, and the emitter is connected with the grounding end. One end of the second resistor R2 is connected with the power input end of the radio frequency switch chip U1, and the other end of the second resistor R2 is connected with the control end. Because the voltage of the grounding end of the radio frequency switch chip U1 changes along with the direct current voltage of the public output end RF-COM, and the control chip for controlling the radio frequency switch chip U1 and the radio frequency switch chip U1 adopt different power supplies and grounds (namely, the voltage system of the input end of the optical coupler U4 is different from the voltage system of the output end), in order to enable the radio frequency switch chip U1 to be normally driven, the optical coupler U4 is arranged between the control chip and the radio frequency switch chip U1 as a driving module, so that the input end and the output end of the optical coupler U4 are effectively isolated, and the normal operation of the radio frequency switch chip U1 can be driven under the condition that the voltage systems of the input end and the output end are not changed is ensured, and therefore, the stability and the reliability of chip driving are remarkably improved.
Specifically, the linear voltage stabilizing module includes a linear voltage stabilizer U3, a third resistor R3, a fourth resistor R4, and a second capacitor C2. The power input end of the linear voltage stabilizer U3 is connected with a first power supply VCC. The power output end of the linear voltage stabilizer U3 is respectively connected with the power input end of the radio frequency switch chip U1 and one end of the fourth resistor R4, and forms a second power supply VDD for supplying power. The other end of the fourth resistor R4 is respectively connected with the adjusting end of the linear voltage stabilizer U3 and one end of the third resistor R3, and the other end of the third resistor R3 is respectively connected with one end of the second capacitor C2 and the reference ground V_GND. The other end of the second capacitor C2 is connected with the power ground, namely the reference ground V_GND is connected with the power ground through the second capacitor C2, the second capacitor C2 is arranged by adopting a high-frequency capacitor and is mainly used for high-frequency signals on the reference ground V_GND, when the high-frequency signals pass through the reference ground V_GND, the impedance of the reference ground V_GND cannot be suddenly changed, and the stability and the reliability of a switching system are effectively improved. Since the adjusting end of the linear voltage stabilizer U3 is connected with the output end of the operational amplifier U2 through the third resistor R3, when the voltage of the output end of the operational amplifier U2 changes due to the change of the dc voltage of the common output end RF-COM of the radio frequency switch chip U1, the voltage difference between the power output end of the linear voltage stabilizer U3 and the adjusting end is a fixed value, so that the power output end of the linear voltage stabilizer U3 changes along with the change of the voltage of the reference ground v_gnd, the voltage difference between the power input end and the ground end of the radio frequency switch chip U1 is unchanged, thereby reducing the fluctuation of the power supply voltage of the radio frequency switch chip U1 and remarkably improving the stability and reliability of the power supply part.
Specifically, the first signal input end RF1 and the second signal input end RF2 of the radio frequency switch chip U1 are respectively connected with an external signal input end, and the common output end RF-COM is connected with an external device signal input end, so as to realize communication between the first signal input end RF1 and the common output end RF-COM, or between the second signal input end RF2 and the common output end RF-COM.
Further, in order to reduce the ac ripple coefficient at the output end of the linear voltage stabilizing module and smooth the dc voltage output, the linear voltage stabilizing module of the present invention further includes a third capacitor C3 for improving the stability of the output voltage of the linear voltage stabilizer U3. One end of the third capacitor C3 is connected with the power output end of the linear voltage stabilizer U3, and the other end of the third capacitor C is connected with power ground. The purpose of this design is to utilize the filter characteristic of the third capacitor C3 to filter out the high frequency spike at the output end of the power supply of the linear voltage regulator U3, so as to stabilize the level of the dc power supply.
In order to improve the universality of the circuit module, the first power supply VCC adopts a power supply with the voltage of 10V, the voltage value is common voltage, the voltage value is suitable for various application circuits, the value of the voltage value is favorable for improving and reforming an old circuit, the reforming difficulty is reduced, the time is saved, and the reforming efficiency can be effectively improved.
As a preferred scheme of the invention, in order to improve the universality of the circuit module, the positive and negative power input ends of the operational amplifier U2 are respectively connected with the power supplies of +5V and-5V power supplies, the voltage value is common voltage, the operational amplifier is suitable for various application circuits, the value of the voltage value is favorable for improving and reforming an old circuit, the reforming difficulty is reduced, the time is saved, and the reforming efficiency can be effectively improved.
As a preferable scheme of the invention, in order to meet the frequency change of the switch from zero hertz to 4 Ghertz, the radio frequency switch chip U1 adopts a PE4245 radio frequency switch chip U1; in order to obtain a better switching effect, the operational amplifier U2 provided by the invention adopts an OPA172 type operational amplifier U2 with good direct current stability and good temperature drift performance; the linear voltage stabilizer U3 provided by the invention adopts the LM1117 linear voltage stabilizer U3 with good power stability, high precision and high efficiency.
As a preferred solution of the present invention, since the linear voltage regulator U3 with the model LM1117 is adopted in the present solution, the voltage difference between the power output terminal and the regulation terminal of the linear voltage regulator U3 is fixed to be 1.25V, in order to fix the voltage difference between the power output terminal of the linear voltage regulator U3 and the reference ground v_gnd to be 3V, the resistance ratio of the third resistor R3 and the fourth resistor R4 is adjusted to be 1.4, and the deduction principle and procedure thereof are as follows:
V out ＝V_GND+(R 3 +R 4 )*I R4 equation 1
The method can be obtained according to the formula 1: v (V) out ＝V_GND+(R 3 +R 4 )*(V out -V adj )/R 4 Equation 2
Wherein: v (V) out For the voltage of the power supply output terminal, V adj To adjust the terminal voltage, V_GND is the reference ground V_GND voltage, R 3 Is a third resistor R3, R 4 For a fourth resistor R4, I R4 For the current flowing through the fourth resistor R4, since Vout-Vadj is a fixed value of 1.25V, the arrangement by substituting formula 2 is obtained:
V out -V_GND＝1.25*(1+R 3 /R 4 ) Equation 3
Since V is required to be maintained in the above out The value of V_GND is 3V, so R is obtained by substitution into the post-finishing 3 /R 4 =1.4, i.e. the ratio of the resistance values of the third resistor R3 and the fourth resistor R4 is 1.4.
The working process and principle of the invention are as follows: the common output end RF-COM of the radio frequency switch chip U1 provided by the invention is connected to the low-pass filter, direct current components in signals are directly fed back to the grounding end of the radio frequency switch chip U1 and the adjusting end of the linear voltage stabilizer U3 through the voltage following action of the operational amplifier U2, so that the voltage of the grounding end becomes the reference ground V-GND and changes along with the change of the direct current voltage, the power output end of the linear voltage stabilizer U3 also changes along with the change of the voltage of the adjusting end, the voltage difference between the power output end and the reference ground V-GND is ensured to be a fixed value, the fact that no direct current voltage difference exists between the common output end RF-COM of the radio frequency switch chip U1 and the grounding end accords with the condition that the direct current bias is zero is achieved, and therefore the processing capacity, stability and reliability of the radio frequency switch chip U1 are remarkably improved, and better switching characteristics are obtained; in addition, because different voltage systems are adopted between the radio frequency switch chip U1 and the control chip, normal driving is realized through the optocoupler module, the stability and the reliability of a driving part can be improved through the design, and the two voltage systems can be effectively isolated, so that the mutual interference is reduced, and the stability and the reliability of the system are effectively improved. The invention also has the advantages of simple structure, low manufacturing cost and small volume.
The above examples are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above examples, and any other changes, modifications, substitutions, combinations, and simplifications that do not depart from the spirit and principle of the present invention should be made in the equivalent manner, and the embodiments are included in the protection scope of the present invention.
Claims (4)
1. The analog switch circuit based on the radio frequency switch chip is characterized by comprising the radio frequency switch chip, a linear voltage stabilizing module for providing stable voltage for the radio frequency switch chip, an operational amplifier module for extracting direct current components of a signal input end, and an optical coupler module for driving the radio frequency switch to work stably; the radio frequency switch chip is respectively connected with the linear voltage stabilizing module, the operational amplifier module and the optocoupler module;
the operational amplifier module comprises an operational amplifier and a low-pass filter for extracting direct current components of output signals; the low-pass filter comprises a first resistor for attenuating the high-frequency signal and a first capacitor for filtering the high-frequency signal; one end of the first resistor is connected with the public output end of the radio frequency switch chip, the other end of the first resistor is respectively connected with the positive input end of the operational amplifier and one end of the first capacitor, and the other end of the first capacitor is connected with the power ground; the positive and negative power supply input ends of the operational amplifier are respectively connected with the positive and negative power supplies; the reverse input end of the operational amplifier is respectively connected with the output end and the grounding end of the radio frequency switch chip, and the grounding end forms reference ground, so that the voltage of the grounding end of the radio frequency switch chip changes along with the change of the direct current voltage of the common output end;
the optocoupler module comprises an optocoupler and a second resistor, wherein the optocoupler is used for driving the radio frequency switch chip; the input end of the optical coupler is respectively connected with the control signal input end and the power ground, and the output end of the optical coupler is respectively connected with the control end and the ground end of the radio frequency switch chip; one end of the second resistor is connected with the power input end of the radio frequency switch chip, and the other end of the second resistor is connected with the control end;
the linear voltage stabilizing module comprises a linear voltage stabilizer, a third resistor, a fourth resistor and a second capacitor; the power input end of the linear voltage stabilizer is connected with a first power supply; the power output end of the linear voltage stabilizer is respectively connected with the power input end of the radio frequency switch chip and one end of the fourth resistor, and forms a second power supply for supplying power; the other end of the fourth resistor is respectively connected with the adjusting end of the linear voltage stabilizer and one end of the third resistor, and the other end of the third resistor is respectively connected with one end of the second capacitor and the reference ground; the other end of the second capacitor is connected with power ground; the voltage of the power supply output end of the linear voltage stabilizer changes along with the change of the reference ground voltage;
the first signal input end and the second signal input end of the radio frequency switch chip are respectively connected with an external signal input end, and the public output end is connected with an external equipment signal input end;
the first power supply adopts a power supply with the voltage of 10V;
the positive and negative power supply input ends of the operational amplifier are respectively connected with power supplies of +5V and-5V power supplies.
2. The radio frequency switch chip based analog switch circuit of claim 1, wherein the linear voltage regulator module further comprises a third capacitor for improving stability of an output voltage of the linear voltage regulator; one end of the third capacitor is connected with the power output end of the linear voltage stabilizer, and the other end of the third capacitor is connected with power ground.
3. The analog switch circuit based on a radio frequency switch chip according to claim 1, wherein the radio frequency switch chip is a PE4245 type radio frequency switch chip, the operational amplifier is an OPAl72 type operational amplifier, and the linear voltage regulator is a LMl 117 type linear voltage regulator.
4. The analog switch circuit of claim 3, wherein the voltage difference between the power output terminal and the adjustment terminal of the linear voltage regulator is 1.25V, the resistance ratio of the third resistor to the fourth resistor is 1.4, and the voltage difference between the power output terminal and the reference ground of the linear voltage regulator is 3V.
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| CN109067386B (en) * | 2018-11-02 | 2023-08-04 | 南京工程学院 | Capacitive touch switch circuit and switch state judging method thereof |
| CN111431514B (en) * | 2020-06-11 | 2020-09-29 | 深圳市鼎阳科技股份有限公司 | Broadband buffering analog switch circuit and integrated circuit |
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| CN107579732A (en) | 2018-01-12 |
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