Ripple noise test system and method
Technical Field
The invention relates to the technical field of server testing, in particular to a ripple noise testing system and method.
Background
The server is used as a high-end computer, can provide services such as cloud computing, mass storage, big data analysis and the like for users in all walks of life, and is an important support for interconnection of everything in the modern society. Due to the high computing speed, long running time, high stability and reliability requirements of the server, the requirements on the hardware circuit quality of the server, especially the quality of the power circuit, are extremely strict. The ripple and the noise are two important parameters for measuring the quality of the power supply circuit, and if the ripple and the noise exceed the electrical specifications of the CPU, the DDR and other key chips, the server may be halted, abnormally restarted and other fatal problems may be caused. With the gradual increase of chip speed and process of CPU, DDR, etc., the supply voltage is also gradually decreasing, so that the design and test requirements for power supply ripple and noise are also stricter.
How to more accurately measure the ripple and noise parameters of the power supply voltage, improve the power supply quality, and ensure the stability and reliability of the operation of the server product is an important concern of hardware engineers.
Currently, the ripple noise test for the server power supply voltage mainly adopts the following methods:
1. the test was performed using a passive probe and an alligator clip ground wire. The method specifically comprises the following steps: the probe is connected to a decoupling capacitor of a power supply network, and the alligator clip is grounded nearby. When the ripple wave is measured, the oscilloscope needs to be set to 20MHz bandwidth limitation, AC coupling and 50 ohm input impedance; for noise measurement, the oscilloscope needs to be set to full bandwidth, AC coupled, 50 ohm input impedance. However, the crocodile clip has a long grounding wire, so that a large loop is formed between the crocodile clip and the probe, a large amount of interference is easily introduced, and the test result is influenced.
2. The passive probe and the grounding spring are used for testing, the testing method is the same as the first mode, and the grounding spring can be used for reducing a loop between the probe and the ground and avoiding introducing other interference. However, since the grounding spring has a certain toughness, it is difficult to actually operate and is liable to fall off, which may cause a short circuit of the circuit board.
3. The testing method is the same as the first mode in that the differential probe and the twisted pair are used for testing, and compared with the crocodile clip ground wire and the grounding spring, the twisted pair has a smaller loop with the probe, so that the external interference is further reduced, and the measurement accuracy of the ripple noise is effectively improved. However, the differential probe is expensive, and needs to pay special attention to the magnitude of the input voltage, otherwise the differential probe is easily damaged; the twisted pair needs to be welded at two ends of the decoupling capacitor, so that the stability of the test operation is ensured, and the test efficiency is not high.
4. And a special ripple probe is used for testing, the testing method is the same as the first mode, and the measuring accuracy is highest. The disadvantages are the special ripple probe, high price and high test cost.
5. The test is carried out by using a 50 ohm coaxial cable and a ripple wave probe self-made by a 100nF isolation capacitor, which is equivalent to the first mode, the shielding layer in the coaxial cable can effectively reduce external interference, improve the measurement precision and has low cost. Because the size of the isolation capacitor is determined, the corresponding cut-off frequency is also fixed, and if the power supply switching frequency of the point to be tested is not consistent with the cut-off frequency, the accuracy of the test result is influenced; cut-off frequency can be changed by manually replacing the isolation capacitor, but the welding level of each person is different, so that the welding quality of the isolation capacitor cannot be guaranteed, and the consistency and the efficiency of testing are influenced.
Disclosure of Invention
In view of the above problems, an object of the present invention is to provide a ripple noise test system and method, which effectively solve the problem that the cut-off frequency of a ripple probe cannot be switched at will, and improve the convenience of the cut-off frequency switching.
In order to achieve the purpose, the invention is realized by the following technical scheme: the utility model provides a ripple noise test system, includes oscilloscope, first coaxial line, second coaxial line and PCB board, be equipped with isolation capacitance switching circuit on the PCB board, oscilloscope and the first end of first coaxial line are connected, and the second end of first coaxial line is connected with isolation capacitance switching circuit's output, and the first end of second coaxial line is connected with isolation capacitance switching circuit's input, and the second end of second coaxial line is equipped with ripple probe subassembly.
Further, the isolation capacitance switching circuit includes: the multi-channel rotary switch comprises a first multi-channel rotary switch S1, a second multi-channel rotary switch S2 and a plurality of isolation capacitors, wherein the output end of the first multi-channel rotary switch S1 is connected with the second end of a first coaxial line, the input end of the second multi-channel rotary switch S2 is connected with the first end of a second coaxial line, and any input end of the first multi-channel rotary switch S1 is connected with the corresponding output end of the second multi-channel rotary switch S2 in series through one isolation capacitor.
Furthermore, ripple probe subassembly includes first metal needle and second metal needle, first metal needle welding is on the inner core of second coaxial line, and the second metal needle welding is on the shielding layer of second coaxial line.
Further, the first coaxial line and the second coaxial line are both 50 Ω coaxial lines.
Further, a BNC connector is arranged at the first end of the first coaxial line, and an SMA connector is arranged at the second end of the first coaxial line.
Furthermore, the first end of the second coaxial line is provided with an SMA connector.
Further, the first multi-way knob switch S1 and the second multi-way knob switch S2 both adopt seven-way knob switches, and the number of the isolation capacitors is seven.
Correspondingly, the invention also discloses a ripple noise testing method, which comprises the following steps:
determining the switching frequency of a power chip of a server to be tested according to a preset power chip manual;
estimating a cut-off frequency corresponding to the switching frequency according to a preset formula, and determining an isolation capacitor to be used; the isolation capacitor to be used is selected to be connected in series between the first coaxial line and the second coaxial line by controlling the isolation capacitor switching circuit;
and setting the oscilloscope in a DC coupling mode, connecting the ripple probe assembly to a decoupling capacitor of a power supply network of the server power supply chip to be tested, and starting a ripple noise test.
Further, the estimating a cutoff frequency corresponding to the switching frequency according to a preset formula and determining the isolation capacitor to be used includes:
estimating the cut-off frequency f corresponding to the switching frequency f according to the calculation formula of the voltage gain G of the high-pass filterL;
The voltage gain G of the high pass filter is calculated as:
wherein, G is 0.9899, which represents the measurement error equal to about 1%; therefore, the switching frequency f is the cut-off frequency fL7 times of the total weight of the composition;
according to the cut-off frequency fLDetermining an isolation capacitor C to be used by using the calculation formula;
cut-off frequency fLThe calculation formula of (2) is as follows: f. ofL=1/(2πRC)
Wherein, R is the input impedance R of the oscilloscope.
Further, the selecting the isolation capacitor to be used by controlling the isolation capacitor switching circuit to be connected in series between the first coaxial line and the second coaxial line specifically comprises:
by adjusting the first multi-way knob switch S1 and the second multi-way knob switch S2, the isolation capacitor to be used is selected to be conducted with the first multi-way knob switch S1 and the second multi-way knob switch S2.
Compared with the prior art, the invention has the beneficial effects that:
1. according to the invention, the PCB is provided with the plurality of isolation capacitors, and the multipath selection is carried out through the knob switch, so that the problem that the cut-off frequency of the self-made ripple probe cannot be switched at will is effectively solved. The design of the double-circuit knob switch can reduce the bifurcation of the signal line, reduce the interference and improve the testing precision.
2. The PCB can set the number of the isolation capacitors according to requirements, and can be replaced by knobs with more switches, so that the expandability of the test system is realized.
3. When the connector is used, different BNC connectors and coaxial cables can be selected according to different oscilloscope interfaces, the connection is convenient, and the test efficiency is improved. Meanwhile, the invention can be suitable for various design occasions of the multi-path selection circuit and has certain universality and flexibility.
Therefore, compared with the prior art, the invention has prominent substantive features and remarkable progress, and the beneficial effects of the implementation are also obvious.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the provided drawings without creative efforts.
FIG. 1 is a system block diagram of the present invention;
FIG. 2 is a flow chart of the method of the present invention;
fig. 3 is an equivalent schematic of the present invention.
In the figure, 1 is an oscilloscope; 2 is a first coaxial line; 3 is a second coaxial line; 4 is a PCB board; 5 is an isolation capacitance switching circuit; 6 is a first metal needle; 7 is a second metal needle; 8 is BNC joint; and 9 is an SMA connector.
Detailed Description
The core of the invention is to provide a ripple noise test system, in the prior art, a 50 ohm coaxial cable and a ripple probe self-made by a 100nF isolation capacitor are used for testing, although a shielding layer in the coaxial cable can effectively reduce external interference, improve the measurement precision and has low cost. However, since the size of the isolation capacitor is determined, the corresponding cut-off frequency is also fixed, and if the power switching frequency of the point to be tested does not accord with the cut-off frequency, the accuracy of the test result is affected; cut-off frequency can be changed by manually replacing the isolation capacitor, but the welding level of each person is different, so that the welding quality of the isolation capacitor cannot be guaranteed, and the consistency and the efficiency of testing are influenced.
According to the ripple noise test system provided by the invention, different BNC connectors and coaxial cables can be selected according to different oscilloscope interfaces; a PCB board is adopted, a plurality of isolation capacitors are placed, knob switches with corresponding paths are configured, and metal needles are respectively welded on a coaxial line inner core and a shielding layer at one end to serve as a test probe and a grounding wire. During actual testing, the switching frequency of a server power supply can be determined according to a power supply chip manual, then the cut-off frequency is estimated according to a formula, so that the size of the isolation capacitor is determined, the corresponding isolation capacitor is selected through the adjusting knob switch S, and therefore ripple noise testing is achieved.
In order that those skilled in the art will better understand the disclosure, the invention will be described in further detail with reference to the accompanying drawings and specific embodiments. It is to be understood that the described embodiments are merely exemplary of the invention, and not restrictive of the full scope of the invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The first embodiment is as follows:
as shown in fig. 1, this embodiment provides a ripple noise test system, which includes an oscilloscope 1, a first coaxial line 2, a second coaxial line 3, and a PCB 4, where the PCB 4 is provided with an isolation capacitor switching circuit 5, the oscilloscope 1 is connected to a first end of the first coaxial line 2, a second end of the first coaxial line 2 is connected to an output end of the isolation capacitor switching circuit 5, a first end of the second coaxial line 3 is connected to an input end of the isolation capacitor switching circuit 5, and a second end of the second coaxial line 2 is provided with a ripple probe assembly.
Wherein, ripple probe subassembly includes first metal needle 6 and second metal needle 7, and first metal needle 6 welds on the inner core of second coaxial line 3, and second metal needle 7 welds on the shielding layer of second coaxial line 3. The first coaxial line 2 and the second coaxial line 3 are both 50 Ω coaxial lines. The first end of the first coaxial line 2 is provided with a BNC connector 8, and the second end of the first coaxial line 2 and the first end of the second coaxial line 3 are both provided with SMA connectors 9.
The isolation capacitance switching circuit includes: the multi-way knob switch comprises a first multi-way knob switch S1, a second multi-way knob switch S2 and an isolation capacitor, wherein seven paths of knob switches are adopted for the multi-way knob switch S1 and the second multi-way knob switch S2, and the number of the isolation capacitors is seven. The output end of the first multi-way knob switch S1 is connected with the second end of the first coaxial line, the input end of the second multi-way knob switch S2 is connected with the first end of the second coaxial line, and any input end of the first multi-way knob switch S1 is connected with the corresponding output end of the second multi-way knob switch S2 in series through an isolation capacitor.
This embodiment provides a ripple noise test system, can select different BNC to connect and coaxial cable according to the oscilloscope interface of difference, set up many isolation capacitors on the PCB board to the form of carrying out the multichannel selection through knob switch has effectively solved the unable problem of switching wantonly of cutoff frequency of self-control ripple probe. The design of the double-circuit knob switch can reduce the bifurcation of the signal line, reduce the interference and improve the testing precision.
Example two:
based on the first embodiment, as shown in fig. 2, the invention further discloses a ripple noise testing method, which specifically includes the following steps:
s1: and determining the switching frequency of the power chip of the server to be tested according to a preset power chip manual.
S2: and estimating the cut-off frequency corresponding to the switching frequency according to a preset formula, and determining the isolation capacitor to be used.
Firstly, estimating a cutoff frequency f corresponding to the switching frequency f according to a calculation formula of a voltage gain G of the high-pass filterL;
The voltage gain G of the high pass filter is calculated as:
wherein, G is 0.9899, which represents the measurement error equal to about 1%; therefore, the switching frequency f is the cut-off frequency fL7 times of the total weight of the powder.
Then, according to the cut-off frequency fLDetermines the isolation capacitance C to be used.
Cut-off frequency fLThe calculation formula of (2) is as follows: f. ofL=1/(2πRC)
Wherein, R is the input impedance R of the oscilloscope. The input impedance R of the oscilloscope is generally selected to be 50 ohms, so that signal reflection is effectively avoided; when the isolation capacitors C are selected to have different sizes, the low-frequency cutoff frequencies fL of the corresponding high-pass filters are different.
When ripple noise is tested, the oscilloscope is set to be in a DC coupling mode, the input impedance is set to be R, and the isolation capacitor is selected to be C through the knob switch, so that the isolation capacitor and the oscilloscope input impedance form a passive high-pass filter, an equivalent schematic diagram is shown in fig. 3, Vin is a power supply signal on a circuit board, and Vout is an AC component of the power supply signal entering the oscilloscope, namely the ripple and the noise of the power supply. Therefore, the cutoff frequency f corresponding to the switching frequency f is estimated using the above-described calculation formula of the voltage gain G of the high-pass filter according to the characteristics of the high-pass filterL,And the isolation capacitance C to be used is determined using a calculation formula up to the frequency fL.
When the voltage gain G is close to 1, Vout is substantially equal to Vin, which is the most accurate measurement. It can be found through calculation that when the frequency f of the signal to be measured is 7fL, the voltage gain G is 0.9899, which indicates that the measurement error is approximately equal to 1%. Therefore, the frequency of the signal to be measured is at least 7 times the cut-off frequency. This can be an important criterion for how to select the isolation capacitance.
S3: the isolation capacitor to be used is selected to be connected in series between the first coaxial line and the second coaxial line by controlling the isolation capacitor switching circuit.
The method comprises the following specific steps: by adjusting the first multi-way knob switch S1 and the second multi-way knob switch S2, the isolation capacitor to be used is selected to be conducted with the first multi-way knob switch S1 and the second multi-way knob switch S2.
Usually, the switching frequency of the power supply chip of the server to be tested is between dozens of KHz and several MHz, and the switching frequency can be determined by inquiring a chip manual. For the selected power supply chip, the knob switches S1 and S2 can be used to select a proper isolation capacitor and set a proper cut-off frequency, so as to more accurately test the ripple and noise parameters of the power supply. The design of the double-circuit knob switch can reduce the bifurcation of the signal line, reduce the interference and improve the testing precision.
S4: and setting the oscilloscope in a DC coupling mode, connecting the ripple probe assembly to a decoupling capacitor of a power supply network of the server power supply chip to be tested, and starting a ripple noise test.
Those of skill would further appreciate that the various illustrative elements and algorithm steps described in connection with the embodiments disclosed herein may be implemented as electronic hardware, computer software, or combinations of both, and that the various illustrative components and steps have been described above generally in terms of their functionality in order to clearly illustrate this interchangeability of hardware and software. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the implementation. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present invention.
Finally, it should also be noted that, herein, relational terms such as first and second, and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Also, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising an … …" does not exclude the presence of other identical elements in a process, method, article, or apparatus that comprises the element.
The ripple noise test system and method provided by the invention are described in detail above. The principles and embodiments of the present invention are explained herein using specific examples, which are presented only to assist in understanding the method and its core concepts. It should be noted that, for those skilled in the art, it is possible to make various improvements and modifications to the present invention without departing from the principle of the present invention, and those improvements and modifications also fall within the scope of the claims of the present invention.