JP2942964B2 - Differential gain and differential phase measuring device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a differential gain and differential phase measuring method for obtaining a differential gain and a differential phase of a digitized signal. In particular, the present invention relates to a measurement method used for testing a characteristic of an A / D converter by obtaining a differential gain and a differential phase of a signal obtained by converting a television signal into digital data by an A / D converter.

(Prior art) In a TV signal, a chrominance signal is superimposed on a luminance signal.
Even if the luminance signal (DC voltage) is changed, the color signal (3.58
MHz) should not have any effect, but in practice, the amplitude (gain) and phase of the chrominance signal change due to changes in the luminance signal due to the characteristics of the circuit that processes the TV signal, and the color The pod color may change. For this reason, it is important to measure and test the differential gain DG and differential phase DP of the processed signal of the television signal in advance. In particular, when a television signal is converted into a digital signal by an A / D converter for digital processing, it is important to know the DG-DP characteristics of the A / D converter.

However, it is difficult to measure the DG-DP characteristics of the A / D converter based on the digitized signal.
The waveform is analyzed using the Fourier analysis technique, and the DG-DP characteristics are measured.

That is, as shown in FIG. 7, a staircase wave signal similar to a luminance signal is used as an input signal, and the ratio of the frequency of the sampling clock to the frequency of the input signal is 4: 1. The data is averaged to obtain data for calculating the cos component and the sin component.

(Problems to be Solved by the Invention) In the above-described conventional technique, since the frequency ratio between the input signal and the sampling clock is fixed at 4, for example, a television signal (video signal) is transmitted at a frequency three times the frequency of a subcarrier. There is a problem that it cannot be used when sampling.

The present invention has been made in order to solve the above-described problems, and is not limited to the fundamental period of the input signal, and the differential gain and the differential phase can be obtained even if the sampling period is shorter than the fundamental period of the input signal. It is an object of the present invention to realize a differential gain and differential phase measurement method capable of obtaining a differential gain and a differential phase without being restricted by a frequency ratio of an input signal and a sampling clock by realizing a calculation method to be obtained. .

(Means for Solving the Problems) The present invention relates to a method for measuring a differential gain and a differential phase of a digitized input signal, wherein the input signal mainly comprises a sine wave having a known frequency. , A differential gain and a differential phase are obtained by the following procedure.

Setting a frequency ratio α of a main component of the input signal and a sampling clock for sampling the input signal and a number M of sampling points required for calculation.

A step of _obtaining coefficients g _ck and g _sk by the following equation using the set frequency ratio α and the number of sampling points M.

Using the obtained coefficients g _ck and g _sk , a cos component Cn and
A step of obtaining a sin component Sn.

A step of obtaining an amplitude g _n and a phase p _n ′ based on the obtained cos component Cn and sin component Sn by using the following equation.

Step of performing the following processing.

P = P + α1, p _n = P + p _n ′, where α1 = 2π · α, a process of repeating the processes from process n to 0 to N−1 (N is the total number of data points).

Amplitude g _n and phase when calculation is performed on all data
step of the final differential gain and differential phase of the p _n.

(Example) Next, an example of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing a configuration example of an apparatus for implementing a method according to the present invention.

In FIG. 1, an A / D converter test device 11 is a device for testing the performance of an A / D converter 1 for converting an input video signal into digital data.
Ramp component removing means 5, initialization processing means 6 for performing initialization processing to obtain coefficients required for calculation, sampling circuit 7, and performing predetermined calculation using the obtained coefficients to obtain differential gain DG and differential It has an operation means 8 for calculating the phase DP, clock generation circuits 2 and 4, a RAM 11 for storing an operation algorithm and various data, and a clock frequency change terminal 9.

The procedure in which the apparatus of FIG. 1 calculates the differential gain and the differential phase of the input signal will be described.

FIG. 2 is a flowchart showing a schematic calculation procedure. The calculation procedure will be described according to the order of steps in the flowchart.

(Step 15) The color signal in the input video signal is represented by the data sequence Xn in FIG.
Is superimposed on the ramp wave as shown in FIG. Here, the ramp wave is a luminance signal. First, a digitized input video signal is stored in the buffer memory 3. Next, the lamp component is removed by the lamp component removing means 5, and the second
Only the carrier component Xn 'as shown in FIG.

(Step 16) M data are sampled from the carrier component Xn ', and the differential gain DG and the differential phase DP are calculated using the coefficients obtained by the initialization processing means 6.

FIG. 3 is a flowchart showing a procedure in which the initialization processing means 6 obtains a coefficient. The calculation procedure will be described according to the order of steps in the flowchart.

(Step 20) First, as shown in FIG. 3, the initialization processing means 6 calculates the frequency ratio α of the input signal (color signal) and the sampling clock for sampling the input signal and the number of sampling points M required for the calculation. Set.

(Step 21) Next, the following calculation is performed to obtain coefficients g _ck and g _sk .

The obtained coefficients g _ck and g _sk are sent to the calculating means 8.

FIG. 4 is a flowchart showing the means by which the calculating means 8 calculates the differential gain DG and the differential phase DP. The calculation procedure will be described according to the order of steps in the flowchart.

(Step 30) The ramp component removing means 5 extracts a linear portion from the ramp data by the least square method, and extracts a sine wave portion by calculating the level difference between the linear portion and the input signal.

(Step 31) Next, the calculating means 8 sets the initial phase p = 0 and the phase difference α1. The phase difference α1 is given by the following equation.

α1 = 2π · α [radian] (Step 32) Using the coefficients g _ck and g _sk , the calculating means 8 obtains a cos component Cn and a sin component Sn by the following equation.

(Step 33) Based on the obtained cos component Cn and sin component Sn, the amplitude is calculated using the following equation.
g _n and phase p _n ′ are obtained.

(Step 34) The following processing is performed.

P = P + α1 _pn = P + _pn ′ (Step 35) The processing of (Step 32) to (Step 34) is repeated from n = 0 to N−1. Here, N is the total number of data points.

(Step 36) Amplitude g _n and phase when calculation is performed for all data
Output _pn as the final differential gain and differential phase.

 Thus, the differential gain and the differential phase are obtained.

In the calculation according to the present invention, when a given input signal has a sine wave component of a known frequency as a main component, a differential gain and a differential phase of the sine wave component are obtained.

The color signal to be measured for the differential gain and the differential phase is a signal obtained by orthogonally exchanging subcarriers whose frequency is strictly determined, and the main component of the signal is a sine wave having a known frequency. Therefore, the differential gain and differential phase of the main component of the color signal can be obtained by the operation of the present invention.

The experimental results according to the present embodiment are shown in FIG. 5 and FIG.

Number of data points N = 256 points, frequency ratio α = 63/256, cos, sin
FIG. 6 shows the result of a simulation performed on an ideal sine wave (FIG. 5) superimposed on a ramp wave with the number of sample points M for calculation being three. In FIG. 5, DG = 2 (%) × (2t−N) ² / N ² (t = 0 to 255,
N = 256) and DP = 2 (deg) × (2t−N) ³ N ³ .

From this result, it can be seen that according to the present embodiment, DG and DP of the color signal can be measured for continuous DG.

(Effects of the Invention) According to the present invention, the following effects can be obtained.

The sampling period is not limited by the fundamental period of the input signal, and the differential gain and the differential phase can be obtained even if the sampling period is shorter than the fundamental period of the input signal.
The sampling period is determined by the frequency ratio between the input signal and the sampling clock. Therefore, in the present invention, the frequency ratio between the input signal and the sampling clock can be set arbitrarily. Thus, the differential phase of the differential gain can be obtained without being restricted by the frequency ratio between the input signal and the sampling clock.

Since the differential gain and the differential phase can be obtained even in a sampling period shorter than the fundamental wave period of the input signal, the differential gain and the differential phase can be obtained with a fine resolution along the time axis direction of the input signal.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration example of an apparatus for carrying out a method according to the present invention. FIGS. 2 to 4 are diagrams showing a procedure for calculating a differential gain and a differential phase. FIG. 6 is a diagram showing experimental results according to the present embodiment, and FIG. 7 is a diagram for explaining a conventional method for measuring differential gain and differential phase. 1 A / D converter, 2, 4 Clock generation circuit, 3 Buffer memory, 5 Lamp component removal means, 6 Initialization processing means, 7 Sampling circuit, 8 Calculation Means 9, 9 Clock frequency change terminal, 10 RAM, 11
… A / D converter test equipment.

Claims (1)

(57) [Claims] 1. A differential gain and differential phase measuring method for obtaining a differential gain and a differential phase of a digitized input signal, comprising the steps of: And measuring a differential gain and a differential phase. Setting a frequency ratio α of a main component of the input signal and a sampling clock for sampling the input signal and a number M of sampling points required for calculation. Using the set frequency ratio α and the number of sampling points M to obtain coefficients g _ck and g _{sk according} to the following equations. Using the obtained _relations g _ck and g _sk , the cos component Cn and si
a step of obtaining an n component Sn; Based on the obtained cos component Cn and sin component Sn,
a step of determining g _n and phase p _n ′. Step of performing the following processing. P = P + α1, p _n = P + p _n ′, where α1 = 2π · α, a process of repeating the processes from process n to 0 to N−1 (N is the total number of data points). Amplitude g _n and phase when calculation is performed on all data
step of the final differential gain and differential phase of the p _n.