JP2009237970A - Loop gain characteristic inspecting method and device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an index for inspecting loop gain characteristics based on gain and phase transition in a main use band in addition to gain margin and phase margin in inspecting loop gain characteristics in a circuit with a negative feedback loop. <P>SOLUTION: A loop gain characteristic inspecting method comprises steps of preparing measured data of loop gain and loop phase difference in a circuit to be inspected (S2), acquiring correlation data by performing correlative operation of the measured data prepared in the step S2 and reference data prepared in advance (S3), acquiring waveform data by carrying out inverse Fourier transformation of the correlation data obtained in the step S3 (S4), and determining that the loop gain characteristics of the circuit to be inspected are poor when amplitude of a predetermined value or more does not exist within a set period in the waveform indicated by waveform data acquired in the step S4 (S5). <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method and apparatus for testing loop gain characteristics in a circuit having a negative feedback loop.

  In many amplifier circuits, switching power supply circuits (switching regulators), series regulators, and the like, negative feedback (NFB) technology that controls a control target based on a result of comparing a target value with an output value is used. Further, in order to evaluate the stability in a circuit having a negative feedback loop, a loop gain characteristic is inspected.

  In order to measure the loop gain characteristics of a circuit having a negative feedback loop, for example, a method using an oscillator and an AC voltmeter, a method using a network analyzer, a method using an FFT analyzer and a signal source, a frequency characteristic analyzer A method using an apparatus such as the above is performed. In general, attention is paid to the loop gain and the loop phase difference as the loop gain characteristics of a circuit having a negative feedback loop.

  FIG. 9 is a diagram illustrating an example of loop gain and loop phase difference in a circuit having a negative feedback loop. In FIG. 9A, the horizontal axis represents the frequency on a logarithmic scale (logf), and the vertical axis represents the absolute value of the loop gain on a logarithmic scale (| Aβ | dB). In FIG. 9B, the horizontal axis represents the frequency on a logarithmic scale (logf), and the vertical axis represents the loop phase difference (∠Aβ).

In this circuit, since the phase of the input signal and the phase of the output signal are inverted, the reference of the loop phase difference is 180 °. In the evaluation of the stability in this circuit, the loop gain (gain margin) at the frequency f ₂ at which the phase rotation margin becomes 0 ° and the phase rotation margin (phase margin) at the frequency f _{1 at} which the loop gain becomes 0 dB Is an indicator. However, when the loop gain characteristics are inspected with two items of gain margin and phase margin, the gain and phase transition in the main use band are not taken into consideration in the determination.

  As a related technique, Patent Document 1 discloses a ghost removing apparatus that can shorten the time required for correlation calculation for detecting a ghost. In this ghost elimination apparatus, the correlator for taking out the sample data stored in the first storage circuit and the sample data stored in the second storage circuit and calculating a correlation function between them is calculated by the first correlator. A first Fourier transform circuit for performing a Fourier transform of the sample data stored in the storage circuit; a second Fourier transform circuit for performing a Fourier transform of the sample data stored in the second storage circuit; and a first Fourier transform. A conjugation circuit that conjugates the output of the circuit, a multiplication circuit that performs multiplication between the output of the second Fourier transform circuit and the output of the conjugation circuit, and an inverse Fourier transform that performs an inverse Fourier transform of the output of the multiplication circuit Circuit.

  Further, Patent Document 2 discloses a ghost removing apparatus that operates stably even when an output waveform having a direct current component is taken into an output waveform memory. In this ghost elimination apparatus, the arithmetic circuit for obtaining the cross-correlation of the waveforms stored in the first and second storage circuits has means for converting two time axis data as two input waveforms into frequency axis data, respectively. Means for zeroing the DC component data contained in the two frequency axis data, means for obtaining correlation value data of the two frequency axis data, and means for converting the correlation value data on the frequency axis to time axis data; Consists of.

Patent Document 1 and Patent Document 2 describe obtaining a cross-correlation between two waveforms, but do not particularly describe checking a loop gain characteristic in a circuit having a negative feedback loop.
JP 63-142778 A (page 1-2, FIG. 1) JP-A-63-318872 (first and third pages, FIG. 1)

  Therefore, in view of the above points, the present invention is based on gains and phase transitions in main use bands in addition to two items of gain margin and phase margin in the inspection of loop gain characteristics in a circuit having a negative feedback loop. An object is to provide an index for inspecting a loop gain characteristic.

  In order to solve the above-described problem, a loop gain characteristic inspection method according to one aspect of the present invention includes a step (a) of preparing measurement data of loop gain and loop phase difference in a circuit under test having a negative feedback loop, Step (b) for obtaining correlation data by performing correlation calculation between the measurement data prepared in (a) and reference data prepared in advance, and inverse Fourier transform of the correlation data obtained in step (b) Step (c) for obtaining waveform data, and in the waveform represented by the waveform data obtained in step (c), if there is no amplitude of a predetermined value or more within a set period, the circuit under test And (d) determining that the loop gain characteristic is poor.

  Here, in step (b), the complex correlation data is obtained by multiplying the complex complex number of the complex measurement data prepared in step (a) and the complex reference data prepared in advance. May be. Further, the loop gain characteristic inspection method has good loop gain characteristics of the circuit under test based on the gain margin and phase margin in the measurement data prepared in step (a) and the determination result in step (d). (E) may be further included.

  Furthermore, a loop gain characteristic inspection apparatus according to one aspect of the present invention is provided with input means for inputting measurement data of loop gain and loop phase difference in a circuit under test having a negative feedback loop from the outside, and input by the input means. Correlation calculation means for obtaining correlation data by performing correlation calculation between measurement data and reference data prepared in advance, and inverse Fourier transformation for obtaining waveform data by performing inverse Fourier transform on the correlation data obtained by the correlation calculation means And the waveform represented by the waveform data obtained by the inverse Fourier transform means, the loop gain characteristic of the circuit to be inspected is defective when there is no amplitude greater than a predetermined value within the set period. Determination means for determining.

  In the present invention, waveform data is obtained by performing inverse Fourier transform on the correlation data obtained by performing the correlation operation between the measurement data and the reference data, and the circuit under test is based on the waveform represented by the waveform data. A loop gain characteristic is determined. Thus, according to the present invention, it is possible to provide an index for inspecting the loop gain characteristic based on the gain and phase transition in the main use band.

Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to the drawings. The same constituent elements are denoted by the same reference numerals, and the description thereof is omitted.
FIG. 1 is a diagram showing a configuration of a loop gain characteristic inspection apparatus according to an embodiment of the present invention. In this embodiment, a circuit to be inspected is a circuit having a negative feedback loop, and includes many amplifier circuits, switching power supply circuits (switching regulators), series regulators, and the like.

  The loop gain characteristic inspection device 20 is used by being connected to an LSI tester 10 having a function equivalent to a frequency analyzer capable of measuring a loop gain and a loop phase difference. By measuring the output signal of the circuit under test while sweeping the frequency of the input signal supplied to the circuit under test having a negative feedback loop using the LSI tester 10, measurement data of the loop gain and loop phase difference is obtained. It is done. This measurement data is input from the LSI tester 10 to the loop gain characteristic inspection apparatus 20 via a cable.

  The loop gain characteristic inspection apparatus 20 includes an input unit 21 such as an interface, a correlation calculation unit 22, an inverse Fourier transform unit 23, a pass / fail determination unit 24, and a storage unit 25. The correlation calculation unit 22 to the pass / fail determination unit 24 are functional blocks representing respective functions, and are realized by a CPU and software (program) in the present embodiment. Software (program) is stored in the storage unit 25. The storage unit 25 is configured by a memory, a hard disk, a flexible disk, an MO, an MT, a CD-ROM, a DVD-ROM, or the like.

  The input unit 21 inputs measurement data of the loop gain and loop phase difference in the circuit under test from the LSI tester 10. The correlation calculation unit 22 obtains correlation data by performing correlation calculation between the measurement data input by the input unit 21 and reference data prepared in advance. The reference data is obtained, for example, by measuring a reference circuit using the LSI tester 10 and stored in the LSI tester 10 or in the storage unit 25.

  The inverse Fourier transform unit 23 obtains waveform data on the time axis by performing inverse Fourier transform on the correlation data obtained by the correlation calculation unit 22. The pass / fail determination unit 24 determines the loop gain characteristics of the circuit under test based on the waveform represented by the waveform data obtained by the inverse Fourier transform unit 23. The determination result of the loop gain characteristic of the circuit under test is stored in the storage unit 25.

Next, a loop gain characteristic inspection method using the loop gain characteristic inspection apparatus shown in FIG. 1 will be described in detail.
FIG. 2 is a diagram showing a loop gain characteristic inspection method according to an embodiment of the present invention.
First, as advance preparation, in step S1, reference data of loop gain and loop phase difference in a reference circuit is prepared. The reference data is obtained, for example, by measuring one or more circuits serving as a reference using the LSI tester 10. When a plurality of measurement values are obtained by measuring a plurality of circuits, an average value of the measurement values can be used as reference data. This reference data may be stored in the LSI tester 10 and read from the LSI tester 10 every time the circuit under test is inspected, or may be stored in the storage unit 25 of the loop gain characteristic inspection apparatus 20. . Alternatively, the reference data may be obtained by simulation.

  Next, in step S2, by using the LSI tester 10 to measure the output signal of the circuit under test while sweeping the frequency of the input signal supplied to the circuit under test, the loop gain and loop level in the circuit under test are measured. Phase difference measurement data is prepared. This measurement data is input from the LSI tester 10 to the input unit 21 of the loop gain characteristic inspection apparatus 20.

  The reference data and the measurement data represent the loop gain and the loop phase difference as shown in FIG. 9 and are treated as a series of complex numbers representing the gain and phase at each frequency in this embodiment.

  In step S3, the correlation calculation unit 22 performs correlation calculation between the measurement data prepared in step S2 and reference data prepared in advance to obtain correlation data. For example, the correlation calculation unit 22 obtains complex correlation data by multiplying the complex complex number of the complex measurement data prepared in step S2 and the complex reference data prepared in advance.

  In step S4, the inverse Fourier transform unit 23 obtains waveform data on the time axis by performing inverse Fourier transform on the correlation data obtained in step S22. When the correlation between the measurement data and the reference data is high, the waveform represented by the obtained waveform data is an impulse waveform. Based on this waveform data, the amplitude of the output signal at each time is obtained.

  3 and 4 are diagrams conceptually showing examples of amplitudes obtained based on waveform data. Here, the magnitude (absolute value) of the waveform at each time point represented by the waveform data is shown as an amplitude. FIG. 3 shows the amplitude when the correlation between the measurement data and the reference data is high. If the correlation between the measurement signal represented by the measurement data and the reference signal represented by the reference data is high, the delay time between these signals is small, so the amplitude at time zero is large, The amplitude at the time decreases and the waveform approaches the impulse waveform.

  On the other hand, FIG. 4 shows the amplitude when the correlation between the measurement data and the reference data is low. If the correlation between the measurement signal represented by the measurement data and the reference signal represented by the reference data is low, the delay time between these signals is large, so the amplitude at time zero is small, The amplitude at time increases and the waveform moves away from the impulse waveform.

In step S5, the pass / fail determination unit 24 determines whether or not the waveform represented by the waveform data obtained in step S4 has an amplitude greater than or equal to a predetermined value within a set period. For example, as shown in FIG. 4, when there is no amplitude equal to or higher than the determination reference level A within the times t _{1 to} t ₂ , it is determined that the loop gain characteristic of the circuit to be inspected is defective. On the other hand, as shown in FIG. 3, when there is an amplitude equal to or higher than the determination reference level A within the times t _{1 to} t ₂ , the process proceeds to step S6.

In step S6, it is determined whether or not the gain margin and the phase margin in the measurement data prepared in step S2 are within a predetermined range. If the gain margin and the phase margin are within the predetermined ranges, it is determined that the loop gain characteristic of the circuit under test is good. If the gain margin or the phase margin is not within the predetermined range, the loop gain characteristic of the circuit under test is determined. Is determined to be defective. For example, in FIG. 9, the loop gain (gain margin) at frequency f ₂ at which the phase rotation margin is 0 ° is 0 dB or less, and the phase rotation margin (phase margin) at frequency f ₁ at which the gain is 0 dB is 0. When it is greater than 180 ° and 180 ° or less, it is determined that the loop gain characteristic of the circuit under test is good.

  As described above, when it is determined in step S5 that there is an amplitude greater than or equal to a predetermined value within the set period, and further in step S6, it is determined that the gain margin and the phase margin are within the predetermined range. As long as the loop gain characteristic of the circuit to be inspected is determined to be good. According to this embodiment, in addition to the two items of gain margin and phase margin, stability can be evaluated based on the gain and phase transition in the main use band, so that the accuracy of inspection can be improved. .

Finally, simulation results for verifying the effectiveness of the loop gain characteristic inspection method according to the present embodiment will be described.
FIG. 5 is a diagram showing the frequency characteristics of the amplitude and phase of the reference signal represented by the reference data, and FIG. 6 is a diagram showing a waveform obtained by autocorrelation calculation of the reference data. That is, assuming that the loop gain and loop phase difference in the circuit under test are equal to the amplitude and phase of the reference signal shown in FIG. 5, the waveform as shown in FIG. 6 is obtained by performing the autocorrelation calculation of the reference data. It is done. As shown in FIG. 6, in the autocorrelation calculation, the amplitude at time zero is large.

  On the other hand, FIG. 7 is a diagram showing the frequency characteristics of the amplitude and phase of the measurement signal represented by the measurement data, and FIG. 8 is a diagram showing a waveform obtained by the correlation calculation between the measurement data and the reference data. . Here, the amplitude and phase of the measurement signal shown in FIG. 7 are greatly different from the amplitude and phase of the reference signal shown in FIG. A waveform as shown in FIG. 8 is obtained by performing a correlation calculation between the measurement data and the reference data. As shown in FIG. 8, in the correlation calculation between signals having different frequency characteristics, the amplitude at time zero is small.

The figure which shows the structure of the loop gain characteristic inspection apparatus which concerns on one Embodiment of this invention. The figure which shows the loop gain characteristic test | inspection method which concerns on one Embodiment of this invention. The figure which shows the example of the amplitude calculated | required based on waveform data conceptually. The figure which shows the example of the amplitude calculated | required based on waveform data conceptually. The figure which shows the frequency characteristic of the amplitude and phase of a reference signal which are represented by the reference data. The figure which shows the waveform obtained by the autocorrelation calculation of the reference data. The figure which shows the frequency characteristic of the amplitude of the measurement signal represented by measurement data, and a phase. The figure which shows the waveform obtained by the correlation calculation of measurement data and reference | standard data. The figure which shows the loop gain and loop phase difference in the circuit which has a negative feedback loop.

Explanation of symbols

  10 LSI tester, 20 loop gain characteristic inspection device, 21 input unit, 22 correlation operation unit, 23 inverse Fourier transform unit, 24 pass / fail judgment unit, 25 storage unit

Claims (4)

Preparing measurement data of loop gain and loop phase difference in a circuit under test having a negative feedback loop;
A step (b) of obtaining correlation data by performing a correlation calculation between the measurement data prepared in step (a) and reference data prepared in advance;
Obtaining waveform data by inverse Fourier transforming the correlation data obtained in step (b);
In the waveform represented by the waveform data obtained in step (c), when the amplitude greater than a predetermined value does not exist within a set period, it is determined that the loop gain characteristic of the circuit under test is defective. Step (d);
A loop gain characteristic inspection method comprising:   The step (b) includes obtaining complex correlation data by multiplying the conjugate complex number of the complex measurement data prepared in step (a) and the complex reference data prepared in advance. Item 4. The loop gain characteristic inspection method according to Item 1.   Step (e) for determining that the loop gain characteristic of the circuit under test is good based on the gain margin and phase margin in the measurement data prepared in Step (a) and the determination result in Step (d) The loop gain characteristic inspection method according to claim 1 or 2, further comprising: Input means for inputting measurement data of loop gain and loop phase difference in a circuit under test having a negative feedback loop from the outside;
Correlation calculation means for obtaining correlation data by performing correlation calculation between the measurement data input by the input means and reference data prepared in advance;
Inverse Fourier transform means for obtaining waveform data by inverse Fourier transforming the correlation data obtained by the correlation computing means;
In the waveform represented by the waveform data obtained by the inverse Fourier transform means, it is determined that the loop gain characteristic of the circuit under test is defective when there is no amplitude greater than a predetermined value within a set period. Determination means to perform,
A loop gain characteristic inspection apparatus comprising: