Overview
As electronic products to sophisticated, miniaturized, low-power direction of sustainable development, the circuit system debugging and verification of analog circuits presented unprecedented challenges. This part of the circuit in the system, usually less than 20% of the weight, but it is often the bottleneck limit the project development process. Although the work of analog circuit fault diagnosis is not a cure-all medicine, but the use of appropriate methods and testing tools can improve debugging efficiency. This ultra-low power circuit through the test, a weak power supply ripple test, on-line measurement of current, short circuit location, noise analysis, and several other examples, combined with a new generation RIGOL 61 / 2 Digital Multimeter DM3068 measured in terms of weak signal advantage of some common fault diagnosis.
Detection of ground loops
Modern electronic products often small-signal analog circuitry, digital circuits and power circuits in a tightly integrated PCB, the circuit layout should not only meet performance requirements, but also by structural design constraints, and to comply with EMC specifications, which gave way circuit layout is a big challenge. Constraints in the multiple constraints, the design phase PCB circuit layout to the existence of uncertainty will need to test during the testing phase.
The circuit shown in Figure 1 as an example, U1, R3, R2-phase amplifier components, design expectations of the amplifier to amplify the input signal Ui 10 times, Uo is the amplifier output voltage. PCB layout as constrained, Ui's "-" input terminals with the resistor R2 between the C-terminal section of wire Rpcb. The PCB may exist on the "circuit X" introduced into the return flow through the wire resistance Ix Rpcb. By the "circuit X" to return Ix impact will be the voltage difference across conductors Rpcb Ue, Ue of the signal in order to determine the impact, need to measure the size of Ue.
Circuit in terms of precision, even if only μV Ue magnitude will have a huge impact on the circuit. DM3068 digital multimeter reading resolution of the minimum DC voltage up to 0.1μV, and measure the terminal with the chassis ground isolation, will not introduce additional DC current to loop to loop suitable for measuring DC error caused by the order of μV.
Note that the weak voltage signal measured thermoelectric power, common mode interference, electromagnetic induction and other error sources, the error is in the order of 10μV, would seriously interfere with the small-signal measurements. Use the same material, or with shielded twisted-pair cable can reduce the testing of thermoelectric power and electromagnetic induction of error. Ue can first determine measurements before the introduction of these error sources the total size of the error, use multimeter "relative" operation exclude the interference of constant error, and then measure the Ue can get more accurate results.
First two tables pen multimeter is connected to terminal C in Figure 1 end, when the multimeter reading is thermoelectric power, common mode interference, electromagnetic induction caused by the error source to observe the changes. If the reading is in a small range of fluctuation is considered to be fixed error. Press the multimeter "relative" menu button, meter will record the current readings, and each subsequent measurement and then subtracting the readings show that fixed the error so that you can eliminate the interference. And then measure the terminals C and Ui's "-" end of the voltage difference between the reading is the exclusion of the Ue disturbance constant error value, you can more accurately reflect the true size of Ue.
Monitoring of power supply fluctuations
If a circuit module as a black box, it will have at least one input port - power. Circuit fault diagnosis, the power port is often forgotten or underestimated, so that some issues were characterized as "Supernatural."
Assume that the black box inside the circuit and the signal inputs are normal, if the black box's output is still a problem, then they should focus on investigation and the power input. Power testing instruments are used oscilloscopes, spectrum analyzers and digital multimeters, they can cover a measuring range of different and should be fully integrated use of these instruments to observe the power signal, to avoid the test blind.
DC instruments are generally considered multimeter, oscilloscope time-domain instruments which belong to the spectrum analyzer is a frequency domain instrument, but the boundaries are being broken. Multimeter has introduced a new generation of time-domain measurements, the following order RIGOL DM3068 digital multimeter multimeter data graphics to introduce the oscilloscope and spectrum analyzer to cover the power test blind.
Figure 3 is an oscilloscope measured modulus of the analog part of hybrid circuits supply voltage waveform, due to a large bandwidth of the oscilloscope, the waveform is a digital circuit introduced in most of the broadband switching noise, amplitude 8.4mVpp. Under normal circumstances, 8.4mVpp power supply ripple and noise meet the people's "psychological expectations", and thus there is no problem on that power (the power of being underestimated.)
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