JPS63109638A - Frequency offset and jitter application circuit - Google Patents

Abstract

PURPOSE:To reduce circuit scale by digitizing an input signal so as to branch a signal into two signal components whose phase difference is nearly 90 deg., multiplying a sinusoidal function and cosine function including frequency offset and jitter with the result and converting the difference of two products into an analog signal. CONSTITUTION:An inputted analog signal is subjected to digital conversion and the output of an analog/digital converter 2 is branched into two signal components whose phase difference is nearly 90 deg.. The product between the two signals and the cosine function and sinusoidal function including the frequency offset and jitter is obtained. A 1st digital multiplier 5 obtaining the product with one output and a 2nd digital multiplier 6 obtaining the product with the other output are used to obtain a difference of both the outputs and the output of the digital subtractor 9 is analog-converted by the digital/analog converter 11. Thus, the circuit scale of the application circuit of frequency offset and jitter is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to frequency offset and shifter application circuits.

The present invention is utilized as a simulator of a digital communication line, and is used to test a modem of a communication device.

〔overview〕

The present invention uses a frequency offset and jitter injection circuit to digitize an input signal, split it into two signal components with a phase difference of approximately 90 degrees, and then apply a cosine function that includes both a frequency offset and a shifter to these two signal components. The circuit size is reduced by multiplying the signal and the signal of the sine function, respectively, and converting the difference between the two products into an analog signal.

[Conventional technology]

Conventionally, in a frequency offset and jitter injecting circuit, a balanced modulator is configured using an analog multiplier, and a frequency offset and jitter are injected by adding phase modulation to an input signal.

FIG. 2 is a block diagram of a conventional frequency offset and jitter injection circuit. The operation of a conventional frequency offset and jitter injecting circuit will be explained with reference to FIG.

Now, assume that the input signal a is a sine wave with a frequency f shown in equation (1).

a = 5in(2πft) ・--
−−−−−−−−41) This signal is input terminal 1 in Figure 2.
, the input signal a undergoes group delay deviation correction in the bandpass filter 23 in advance in the equalization layer 21, and is input into the balanced modulator 22 using an analog multiplier. If the output of the modulation signal generator 28 is the modulation signal of frequency f0 shown in equation (2), then b = 5in (2rt f o t )
------- (2) At the output of the balanced modulator 22, a double-side band signal C shown in equation (3) appears.

c= −(cos(2ycf−2πf,)t−cos(
2rc f + 2 rt f o) t ) --
---------- (3) The double-side band signal C is passed through the bandpass filter 23 and becomes the upper side band signal d shown in equation (4), which is input to the balanced modulator 24 using an analog multiplier. .

d= −−cos(2πf+2πfo)t・−−111−−・−・−(4) At this time, the output of the demodulation signal generator 29 is modulated with a frequency f as shown in equation (5). Assuming that the demodulated signal eφ has a phase change of φ with respect to
(πfI, t+φ) ------- Curve (5) At the output of the balanced modulator 24, a double-side band signal gφ shown in equation (6) appears.

gp = (sin(2πf -φ) - 5in
((2πf+4πfJt+φ)]・−・・・−・・−
・(6) The lower side band is extracted from the double side band signal by the low pass filter 25, the group delay distortion is corrected by the equalization layer 26, and the amplifier 27
If amplitude correction is added to the input signal a shown in equation (7),
In contrast, an output signal hφ whose phase is shifted by φ is obtained.

hp -5in (2* f t-φ) ・
(7) Furthermore, if the output of the demodulated signal generator 29 is the demodulated signal eΔ shifted by Δf0 as shown in equation (8), then 8A=sin(2πf0+2πΔf
o) t ・---------(8) Balanced modulator 24
A double-side band signal gΔ shown in equation (9) appears in the output direction.

gΔ= (sin (2yc(f−Δf O)
t)-5in (2πf+4πfo+2πΔf o)
t)・・・−・・−−−・(9) If group delay correction and amplitude correction are added in the same way as for the double-sideband signal gφ, the frequency will be Δf and Tak for the input signal a shown in 200. A shifted output signal hΔ is obtained.

hl −5in (2π(f−Δfo) t )
...--------=arp This allows frequency offset and jitter to be applied to the input signal.

[Problem that the invention seeks to solve]

However, in such conventional frequency offset and jitter injection circuits, all processing is performed on analog signals, so an equalization layer that corrects group delay distortion, a balanced modulator using an analog multiplier, a bandpass filter, and a modulation signal generator and demodulation signal generator are required. In particular, a bandpass filter is a large-scale filter because it is used to extract the upper sideband of a double-sideband signal that has been subjected to amplitude modulation. Therefore, there was a drawback that the scale of the entire circuit became large.

The present invention solves the above-mentioned drawbacks, and aims to provide a frequency offset and jitter injection circuit with a small circuit scale.

[Means for solving problems]

The present invention consists of an analog-to-digital converter that converts an input analog signal into a digital signal, and two phase difference filters that separate the output of the analog-to-digital converter into two signal components with a phase difference of approximately 90 degrees. a cosine function generator that generates a cosine function signal including a frequency offset and jitter, and a sine function generator that generates a sine function signal with a predetermined phase difference with respect to the cosine function signal.
a first digital multiplier that calculates the product of the cosine function signal and the output of one of the two phase difference wave filters corresponding to this signal; a second digital multiplier for calculating the product with the other output of the phase difference wave filter; and a digital subtracter for calculating the difference between the output of the first digital multiplier and the output of the second digital multiplier. , and a digital-to-analog converter that converts the output of the digital subtracter into analog.

[For production]

An analog-to-digital converter converts human analog signals into digital ones. Two 90-degree phase differential wave filters separate the output of the analog-to-digital converter into two signal components whose phases differ by approximately 90 degrees from each other. A cosine function generator generates a cosine function signal including a frequency offset and a shifter.

A sine function generator generates a sine function signal having a predetermined phase difference with respect to this cosine function signal. The first digital multiplier calculates the product of the cosine function signal and one output of the 90-degree phase difference wave filter corresponding to this signal. A second digital multiplier divides the signal of the sine function and the 9 corresponding to this signal.
Find the product with the other output of the 0 degree phase difference wave filter. A digital subtracter calculates the difference between the output of the first digital multiplier and the output of the second digital multiplier. A digital-to-analog converter converts the output of the digital subtracter to analog. The above operation allows the circuit scale to be reduced.

〔Example〕

Embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram of a frequency offsetting circuit and jitter injecting circuit according to an embodiment of the present invention. In Figure 1, an analog input signal x (t) from outside the diagram is input to input terminal 1.
is connected to the input of the analog-to-digital converter 2 via. Digital signals from the analog/digital modulator 2 are respectively connected to inputs of 90-degree phase difference wave filters 3.4 composed of digital filters.

Outputs having a phase difference of approximately 90 degrees from the outputs of the 90 degree phase difference wave filter 3 and the 90 degree phase difference wave filter 4 are connected to one input of the digital multiplier 5 . Also, from the cosine function generator 7, a frequency offset φ0 and a shifter Δ
A cosine signal cos (2πΔf, t+φ
. ) is connected to the other input of the digital multiplier 5.

The digital multiplier 5 calculates the product of the output of the 90-degree phase difference wave filter 3 and the cosine signal cos(2πΔfat+φ.).

On the other hand, the output of the 90-degree phase difference wave filter 4 is connected to one input of the digital multiplier 6. Also, the frequency offset) φ from the sine function generator 8. A sine signal 5in (2πΔf, t+φ,) containing both jitter Δf and jitter Δf is connected to the other input of the digital multiplier 6. The digital multiplier 6 calculates the product of the output of the 90-degree phase difference wave filter 4 and the sine signal 5in (2πΔf0t+φ.). The output of the digital multiplier 5.6 is the output of the digital subtracter 9.
are connected to their respective inputs. A digital subtracter 9 determines the difference between the outputs of the digital multiplier 5.6. The output of the digital subtracter 9 is connected to the input of the group delay equalization layer 10. In the 0 group delay equalizer IO, the group delay distortion of the input is equalized. The output of the 0 group delay equalizer 10 is digital/analog. Connected to the input of converter 11. The input signal x (frequency offset φ with respect to tl and jitter Δf) from the digital-to-analog converter 11.

An analog output signal F (t) applied to the output terminal is connected to the output terminal.

The operation of the frequency offset and jitter applying circuit having such a configuration will be explained. Now, for easy explanation, the input signal x (t) is expressed as 2OB.

x (t) = cos(2ft f t )
−=−−・QυThis input signal x (Δ in tl
Jitter (frequency deviation) f0, φ. The output signal y (t) given the frequency offset (phase shift) can be expressed as 2〇.

y(tl=cos (2π(f+Δf,)t+φ.)=
cos(2yc f t)Xcos(2πΔf, t+φ
. )−sin(2πf t)Xsin(2ffΔf, t
+φ. )・−・−・−・−・−03 As a result, if the input signal x (tl is split into signals with a phase difference of 90 degrees, it can be directly It can be seen that the frequency offset φ. and the jitter Δf0 can be applied.

When a 90 degree phase difference filter is used, equation (2) becomes equation (2
)become that way.

y(t)−(h+*x(t)) Xcos(2πΔfo
t+φ)−(11, umbrella x(t)) xsin(2πΔ
rot + φ)−・−・−−−−−−(2) Here, * represents a convolution operation. And hl and h2 are the impulse response functions of the phase difference wave filter, and if their respective Fourier transforms are H + (jw) and Hz (jw), the amplitude characteristics and phase characteristics are as shown in equations (b) and (to). become.

! H+(j w) I = l Hz(j w) l
King 1... (b) arg H, (jw) -ar
g Hz (jW) = -□1...------- (To) In Fig. 1, the input signal x applied to input terminal 1
(t) is digitized by the analog-to-digital converter 2 and input to a 90-degree phase difference wave filter 3.4 constituted by a digital filter.

The output of the 90 degree phase difference wave filter 3, which has a phase difference of approximately 90 degrees with respect to the output of the 90 degree phase difference wave filter 4, is input to the digital multiplier 5, and the frequency offset φ shown in equation (to) is input to the digital multiplier 5. . and the output of the cosine function generator 7, which includes both the shifter Δf0 and the shifter Δf0. On the other hand, the output of the 90-degree phase difference wave filter 4 is input to the digital multiplier 6, and the frequency offset φ shown in equation (2) is generated. The product of the output of the sine function generator 8 containing both the jitter Δf and the jitter Δf is determined.

The difference between the respective products is calculated by the digital subtractor 9, the group delay distortion of the signal is equalized by the group delay etc. vase 10, and the input signal x (t) is passed through the digital-to-analog converter 11.
An analog output signal y (t) with a frequency offset and jitter applied thereto is obtained at the output terminal 12 .

〔Effect of the invention〕

As explained above, the present invention includes an analog/digital modulator, a 90 degree phase difference wave filter, a digital multiplier,
By providing a digital subtracter, a cosine function generator, a sine function generator and a digital-to-analog converter,
This has the excellent effect of reducing the circuit scale of the frequency offset and jitter application circuit.

The circuit of the present invention is effective when used to configure a simulator of an actual line for testing modem equipment.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a frequency offset and jitter injection circuit according to an embodiment of the present invention. FIG. 2 is a block diagram of a conventional frequency offset and jitter injection circuit. DESCRIPTION OF SYMBOLS 1... Input terminal, 2... Analog-digital converter (A/D converter), 3.4... 90 degree phase difference wave filter, 5.6... Digital multiplier, 7... ... Cosine function generator, 8 ... Sine function generator, 9 ... Digital subtractor, 10 ... Group delay equalizer, 11 ... Digital-to-analog converter (D/A converter) , 12... Output terminal, 21... Equal flower vase, 22.24... Balanced modulator using analog multiplier, 23... Bandpass filter, 25
...Low pass filter, 26...Vase, 27...Amplifier, 2nd...Modulation signal generator, 29...Demodulation signal generator.

Claims (1)

[Claims] (1) An analog-to-digital converter that converts the input analog signal to digital, and two phase difference wave filters that separate the output of this analog-to-digital converter into two signal components with a phase difference of approximately 90 degrees. a cosine function generator that generates a cosine function signal including a frequency offset and jitter; a sine function generator that generates a sine function signal with a predetermined phase difference with respect to the cosine function signal; a first digital multiplier that calculates the product of the signal of the sine function and the output of one of the two phase difference wave filters corresponding to this signal; and the signal of the sine function and the two phase difference waves corresponding to this signal. a second digital multiplier for calculating the product with the other output of the filter; a digital subtracter for calculating the difference between the output of the first digital multiplier and the output of the second digital multiplier; A frequency offset and jitter injection circuit comprising a digital-to-analog converter that converts the output of the subtracter into analog.