JPS63119349A - Four-phase psk modulator - Google Patents

Abstract

PURPOSE:To eliminate a need of harmonic eliminating low-pass filters and obtain four-phase PSK (phase shift keying) signals whose phase arrangement is not changed and error rate characteristic is good, by providing a distortion correcting circuit to obtain the output which can correct the distortion of an analog multiplier. CONSTITUTION:A distortion correcting circuit 12 consists of an attenuating circuit 15 which attenuates a prescribed carrier signal from a carrier signal generating circuit 5 up to a prescribed level, an analog multiplier 16 which has the same input/output characteristic as an analog multiplier 6 and multiplies the output of a DC voltage generating circuit 17 and that of the attenuating circuit 15, and a differential amplifier 18 which subtracts the output of the analog multiplier 16 from the carrier signal to output a correction carrier signal. A distortion correcting circuit 13 is constituted similarly. Since outputs are obtained which can correct distortions of analog multipliers 6 and 8, harmonic components are eliminated from outputs of analog multipliers 6 and 8 and harmonic eliminating low-pass filters are unnecessary, thereby obtaining four- phase PSK signals whose phase arrangement is not changed and error rate characteristic is good.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a four-phase PSK modulator, and in particular to a four-phase PSK modulator used for subchannel modulation for broadcasting.
Regarding Kay modulators.

[Conventional technology]

Conventionally, 4-phase PSK (phase 5-hift keyin) was used for this type of sub-channel modulation for broadcasting.
g; PSK) As shown in FIG. 3, the modulator has input terminals 1 and 2 that input the first or second digital signal ASB, and the Low-pass filters 3 and 4 that limit the bands of digital signals A and B, a carrier signal generation circuit 5 that sends out a carrier signal, and the output of the low-pass filter 3 and the carrier signal that is the output of the carrier signal generation circuit 5 are multiplied. An analog multiplier 6, a 90 degree phase shifter 7 that shifts the phase of the carrier signal from the carrier signal generation circuit 5 by 90 degrees, and an analog multiplier that multiplies the output of the low-pass filter 4 and the output of the 90 degree phase shifter 7. It is comprised of a multiplier 8, an adder circuit 9 that adds the respective outputs of the analog multiplier 6 and the analog multiplier 8, and a low-pass filter 10 that removes harmonic components of the four-phase PSK modulated signal. The signal that has passed through the low-pass filter 10 is output from an output terminal 11.

Now, assuming that the carrier signal is COS ωt, the first digital signal A applied to the input terminal 1 is band-limited by the low-pass filter 3 and then applied to the analog multiplier 6. The output of the analog multiplier 6 is P of the following equation.
+, Po is obtained.

(i) When the first digital signal A is 1, PI = 1
1CO8ωt = COS ωt (1) (]ii When the first digital signal A is −・l, Po
= −l −cos w t = −COS ω t (2) Similarly, the second digital signal B whose band is limited by the low-pass filter 4 is phase-shifted by the 90-degree phase shifter 7. (Here, we take a case where the phase is delayed by 90 degrees as an example) and is multiplied by the carrier signal in an analog multiplier 8.

As the output of the analog multiplier 8, Ql and Qo of the following equations are obtained.

<i) When the second digital signal B is 1 = sin
ω t ...... (3) (ii) When the second digital signal B is -1 =
-5in ω t (4) The outputs of these analog multipliers 6 and 8 are added by an adder circuit 9. As outputs of the adder circuit 9, TSU, V, and W of the following equations are obtained. here = si
Let n rr / 4 = cos rr / 4.

(i) T=PI+Q.

= cos w t -5in ω t...
・・・ (5〉 (11) U = P 6 + Q 6 = -
CO8(11t −5in ωt・・・・・・(
6) (i+i) V = Po 10+= -cos
ωt +sin ωt... (7) (iv) W=P, +Q.

= cos ωt + sin ωt・・・・・・
(8) In this way, a four-phase PSK modulated signal with a Daley code arrangement was obtained.

[Problem that the invention seeks to solve]

The conventional four-phase PSK modulator described above has an analog multiplier 6
．． This can be realized by using an ideal analog multiplier that does not generate any waveform distortion. however,
In the actual analog multiplier 6.8, the output characteristics are non-linear due to problems with the device itself, and the frequency characteristics (frequency vs. gain characteristics) are also not flat. Therefore, the input signal
In particular, the carrier signal is distorted to generate harmonic components, and the harmonic components are multiplied by the band-limited digital signal to generate harmonic components of the four-phase PSK modulated signal.

Therefore, in the conventional 4-phase PSK modulator, a low-pass filter 1 is used to remove the harmonic components of the 4-phase PSK modulated signal.
0 is required. Therefore, the circuit becomes complicated, and the phase arrangement of the four-phase PSK modulated signal changes due to the phase rotation of the low-pass filter 10, resulting in deterioration of error rate characteristics.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to prevent the circuit from becoming complicated.
Moreover, the phase arrangement does not change and the error rate characteristics are good.
An object of the present invention is to provide a four-phase PSK modulator that can obtain an SK signal.

[Means for solving problems]

The four-phase PSK modulator of the present invention includes: (1) a carrier signal generation circuit that generates and outputs a predetermined carrier signal; and (2) a first attenuation circuit that attenuates the predetermined carrier signal from this carrier signal generation circuit to a predetermined value. , a first analog multiplier that multiplies the carrier signal from the first attenuation circuit by a predetermined DC voltage, and a first correction by subtracting the output of the first analog multiplier from the predetermined carrier signal. a first distortion correction circuit having a first differential amplifier that outputs as a carrier signal; and (1) a 90-degree phase shift circuit that receives the above-mentioned predetermined carrier signal and sends out a signal that is 90 degrees different in phase from the carrier signal. a second attenuation circuit that attenuates the output signal from this 90-degree phase shifter to a predetermined value; and a second analog that multiplies the output signal of this second attenuation circuit by a predetermined DC voltage. a second distortion correction circuit having a multiplier and a second differential amplifier that subtracts the output of the second analog multiplier from the output signal of the 90-degree phase shifter and outputs it as a second correction carrier signal; and ■ a third signal that multiplies the first digital signal band-limited by the low-pass filter and the first corrected carrier signal from the first distortion correction circuit.
(1) a fourth analog multiplier that multiplies the second digital signal band-limited by the low-pass filter and the second corrected carrier signal from the second distortion correction circuit; (2) these third analog multipliers; and an addition circuit that adds each output of the fourth analog multiplier.

Therefore, harmonic components are removed from the output of the adder circuit, and there is no need to pass the output of the adder circuit through a low-pass filter. Therefore, the circuit is not complicated, and by not using a low-pass filter for removing harmonics, it is possible to obtain a four-phase PSK signal with good error rate characteristics without changing the phase arrangement.

〔Example〕

Next, an embodiment of the present invention will be described using FIGS. 1 and 2.

FIG. 1 shows an embodiment of a 4-phase PSK modulator according to the present invention, and is particularly used for broadcasting subchannel modulation.
Let us take the case of a phase PSK modulator as an example. In this figure, the same reference numerals are used for the same or corresponding parts as in FIG. 3.

This four-phase PSK modulator has input terminals 1 and 2, respectively.
low-pass filters 3 and 4 that limit the bands of the first digital signal A and second digital signal B applied to the carrier signal generation port 't!' that generates and sends out a predetermined carrier signal. ! 5, a 90 degree phase shifter 7 which shifts the phase of a predetermined carrier signal from the carrier signal generation circuit 5 by 90 degrees, and a predetermined carrier signal from the carrier signal generation circuit 5 is supplied to generate a first corrected carrier signal. A first distortion correction circuit 12 that transmits a signal, a second distortion correction circuit 13 that inputs the output signal of the 90-degree phase shifter 7 and sends out a second correction carrier signal, and a an analog multiplier 6 as a third analog multiplier that multiplies the first digital signal A by the first corrected carrier signal;
, an analog multiplier 8 as a fourth analog multiplier that multiplies the second digital signal B band-limited by the low-pass filter 4 and the second corrected carrier signal, and these analog multipliers 6 and 8, and an adder circuit 9 for adding the respective outputs of 8.

Here, the first and second distortion correction circuits 12 and 13 are
These first and second distortion correction circuits 1 are for correcting distortion of analog multipliers 6 and 8, respectively.
2 and 13 are each constructed as shown in FIG.

That is, the first distortion correction circuit 12 includes a first attenuation circuit 15 that attenuates a predetermined carrier signal from the carrier signal generation circuit 5 supplied via the input terminal 14 to a predetermined level, and an analog multiplier 6. have the same input and output characteristics,
a first analog multiplier 16 that multiplies the output of the DC voltage generation circuit 17 and the output of the first attenuation circuit 15;
The output of the analog multiplier 16 is subtracted from the above carrier signal and output to the output terminal 19 as a first corrected carrier signal.
and a tenth differential amplifier 18 which outputs an output from the differential amplifier 18.

Similarly, the second distortion correction circuit 13 includes a second attenuation circuit 15' that attenuates the output signal from the 90-degree phase shifter 7 supplied via the input terminal 14' to a predetermined level, and an analog multiplier. a second analog multiplier 16' which has the same output characteristics as 8 and which multiplies the output of the DC voltage generation circuit 17' and the output of the second attenuation circuit 15'; and this second analog multiplier 16'. 16' from the output signal of the 90-degree phase shifter 7 and outputs it from the output terminal 19' as a second corrected carrier signal.

Now, assuming that the carrier signal generated by the carrier signal generation circuit 5 is X, this carrier signal X is supplied to the input terminal 14 of the first distortion correction circuit 12.

The carrier signal X applied to the input terminal 14 is applied to the positive input terminal of the first differential amplifier 18 and simultaneously applied to the first attenuation circuit 15 . After the carrier signal X is attenuated to 1/k by the first attenuation circuit 15, it is applied to the first analog multiplier 16. This first analog multiplier 16 multiplies by a specified level, in this case a unit voltage "1" generated by the DC voltage generating circuit 17, and from the non-linearity of the first analog multiplier 16, the following formula obtain.

However, for the convenience of explanation, the distortion components are assumed to be up to the third order.

D= -a x+ b x" + c x'...
-(9) Here, aSb and c are each constants.

This signal is applied to the negative input terminal of the first differential amplifier 18, and an output X' expressed by the following equation is obtained.

・・・・・・(10) Now, if a=1, equation (10) becomes as follows.

(11) Carrier signal for distortion correction obtained by the first distortion correction circuit 12 as described above (first correction carrier signal)
x′ is multiplied by the first digital signal A band-limited by the low-pass filter 3 and the analog multiplier 6;
As an output, the following formula % formula % (i) When the first digital signal Δ is 1, P+ '=
1 ・(x'+bx2+cx')bx2 +cx' (12) and P,'=cos ωt (13) (11) Similarly, the first digital signal A is is -1
When, P,'=-1-(x'+bx2 +CX')=-
cos ω t (14) Further, the predetermined carrier signal X from the carrier signal generation circuit 5 is phase-shifted by 90 degrees by the 90-degree phase shifter 7, (For example, take the case where
It is applied to the input terminal 14' of the second distortion correction circuit 13.

Here, if the output of the 90 degree phase shifter 7 is y, then Than, It is.

Therefore, like the first distortion correction circuit 12 described above, the second distortion correction circuit 13 obtains as an output a carrier signal (second correction carrier signal) y' for distortion correction shown in the following equation.

・・・・・・(15) Here, b' and C' are constants.

The second digital signal B band-limited by the low-pass filter 4 is multiplied by the second corrected carrier signal y′ from the second distortion correction circuit 13 in the analog multiplier 8.
QI' and Qo' of the following equations are obtained as outputs.

(i) When the second digital signal B is 1, Q +'=
1・(y'+b'y2+c'y3)=sin ωt
......(16) (ii) When the second digital signal B is -1, Q o""1'
(y'10"y' + C"l3) = -5in
ω t (17) The respective outputs of these analog multipliers 6 and 8 are added by an adder circuit 9, and the outputs are T' and U as shown below.
', y', and W' are obtained. Here, L=sin π
/ 4 = cos yr / 4.

(i) T'=P, '+Q,' =cos ωt -5in ωt・・・・・・(
18) (ii) U'=P, '10Q,'=-cos
ωt -5in ωt...(19) (iii) V'=Pa'+Q+'=
-CO3(11t +sin w t...
...(20) (IV) W' = P + ' + Q+
'=cos 6D t +sin w t
(21) That is, the predetermined carrier signal X that is the output of the carrier signal generator 5 is expressed as X = 1 / (1-1/k) cos co
By setting t to 4 of the Daley code arrangement as above,
A phase PSK modulated signal can be obtained.

As described above, the first and second
distortion correction circuits 12 and 13 are provided, and an analog multiplier 6
Since the outputs that can correct (cancel out) the distortions of analog multipliers 6 and 8 are set to i, harmonic components are removed from the outputs of analog multipliers 6 and 8. Therefore, there is no need to further pass the output of the adder circuit 9 through a conventional low-pass filter for removing harmonics, and therefore the circuit does not need to be complicated. Furthermore, since it is not necessary to use a low-pass filter for removing harmonics in this way, the phase arrangement does not change, and a four-phase PSK signal with good error rate characteristics can be obtained.

In the embodiments described above, the first and second analog multipliers 16 and 16' have been described as having the same output characteristics as the corresponding analog multipliers 6 and 8, respectively. When the analog multiplier 8 has the same input/output characteristics, the first and second analog multipliers 16 and 16' have the same input/output characteristics, and the above-mentioned y/, Q, /, QO
'Formula %Formula % Furthermore, the present invention is not limited to the present embodiment, and various applications and modifications can be considered without departing from the gist of the present invention.

〔Effect of the invention〕

As described above, if the four-phase PSK modulator of the present invention is used, the outputs of the third and fourth analog multipliers do not contain high subwave components, so a conventional low-pass filter for removing harmonics can be used. No longer needed. Therefore, the circuit does not need to be complicated, and it is possible to obtain a four-phase PSK signal with good error rate characteristics without changing the phase arrangement.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of a four-phase PSK modulator according to the present invention, and FIG. 2 is a distortion correction circuit 12 shown in FIG.
．． A block diagram showing an example of 13, Fig. 3 is a conventional 4-phase P
FIG. 2 is a block diagram showing an example of an SK modulator. 3.4...Low pass filter, 5...
Carrier signal generation circuit, 6... Analog multiplier (third analog multiplier), 7... 90 degree phase shifter, 8... Analog multiplier (fourth analog multiplier) analog multiplier), 9...Addition circuit, 12...First distortion correction circuit, 13...Second distortion correction circuit, 15...・First attenuation circuit, 15'... Second attenuation circuit, 1-6... First analog multiplier, 16'...
...Second analog multiplier, 18...First
differential amplifier, 18'... second differential amplifier. Applicant: NEC Corporation Representative

Claims (1)

[Claims] 1. A carrier signal generation circuit that generates and outputs a predetermined carrier signal, a first attenuation circuit that attenuates the predetermined carrier signal from this carrier signal generation circuit to a predetermined value, and a carrier from this first attenuation circuit. a first analog multiplier that multiplies the signal by a predetermined DC voltage; and a first differential amplifier that subtracts the output of the first analog multiplier from the predetermined carrier signal and outputs it as a first corrected carrier signal. a 90 degree phase shifter that receives the predetermined carrier signal and outputs a signal having a phase different by 90 degrees from the carrier signal; and an output signal from the 90 degree phase shifter. a second attenuation circuit that attenuates the output signal of the second attenuation circuit to a predetermined value; a second analog multiplier that multiplies the output signal of the second attenuation circuit by a predetermined DC voltage; a second distortion correction circuit having a second differential amplifier that subtracts the signal from the output signal of the 90-degree phase shifter and outputs it as a second correction carrier signal; a first digital signal band-limited by a low-pass filter; 1st
a third analog multiplier that multiplies a first corrected carrier signal from the distortion correction circuit, and a second digital signal band-limited by the low-pass filter and a second correction signal from the second distortion correction circuit. A four-phase PSK modulator comprising: a fourth analog multiplier that multiplies a carrier signal; and an adder circuit that adds the respective outputs of the third and fourth analog multipliers. .