JPH0425744B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a circuit for delay detection of a signal subjected to four-phase phase modulation, and particularly to a detection circuit suitable for integration into an integrated circuit.

Conventionally known delay detection circuits are used in intermediate frequency bands and have the disadvantage of being unsuitable for integration into integrated circuits.

An object of the present invention is to provide a delay detection circuit that eliminates such drawbacks and performs signal processing in the baseband band, thereby facilitating integration into an integrated circuit.

According to the present invention, the first quadrature detector uses a four-phase modulated wave as an input signal and uses a signal obtained from the output of a local oscillator having an oscillation frequency approximately equal to the center frequency of the input modulated wave as a local oscillation signal. and,
On the other hand, a second quadrature detector whose relative phase differs by an odd multiple of 45° is provided, two baseband signals output from the first quadrature detector are used as first and second signals, and the The two orthogonal baseband signals output from the second orthogonal detector are
when the third and fourth signals each have a delay different from the first and second signals by the symbol period of the four-phase modulated wave, and the first A signal obtained by multiplying the signal and the third signal is defined as a fifth signal, a signal obtained by multiplying the second signal and the fourth signal is defined as a sixth signal, and a signal obtained by multiplying the signal by the fourth signal is defined as a sixth signal. A signal obtained by multiplying the signal by the third signal is set as a seventh signal, a signal obtained by multiplying the second signal and the third signal is set as an eighth signal,
A signal obtained by adding the fifth signal and the sixth signal is binarized, this is used as a first detection signal, and the seventh signal and the eighth signal are subtracted. Binarize the signal obtained from the
The above object can be achieved by using a detection signal as a detection signal and using a four-value signal obtained from a combination of the first and second detection signals as a detection output signal.

A detailed explanation will be given below using the drawings.

FIG. 1 is a block diagram showing an embodiment of the present invention. A phase modulated wave as shown in FIG. 2 on a complex amplitude plane is input to the input terminal in the figure. Such a modulated wave is known as a four-phase modulated wave, and the phase of the carrier wave is determined by a four-value transmission signal at one of the points indicated by circles in the figure. The phase change at successive symbol times is one of 0°, ±90°, and 180°, and differential detection means detecting these four types of phase changes.

A phase modulated wave is generally expressed as follows.

V(t)=A(t)cos[Wct+P(t)...(1) Here, A(t) is the amplitude (A(t)≧0), Wc is the center angular frequency of the modulated wave, P(t ) is the phase determined by the modulating input signal. This modulated input signal is branched into two signals: one is input as is, and the other is delayed by the delay circuit 5 and then input. The output of the local oscillator 2 in FIG.
That is, it is separated into pairs of 0° and 90° and 45° and 135°. The four branched input signals are frequency-converted to the baseband band by mixers 31, 32, 33, and 34, respectively, and are separated into four local oscillation signals corresponding to the four local oscillation signals, and are used to limit noise and remove interference waves. low pass filters 41, 42, 43, 44
is input. The output signals can be respectively expressed as follows.

γ ₁ (t)=A(t)Bcos[P(t)+ΔQ(t)] ……(2) γ ₂ (t)=A(t)Bsin[P(t)+ΔQ(t)] ……( 3) γ ₃ (t)=A(t-T)Bcos [P(t-T)+ΔQ(t
−T)+45°−WcT ……(4) γ ₄ (t)=A(t−T)Bsin[P(t−T)+ΔQ
(t-T)+45°-WcT...(5) Here, B is a constant, and ΔQ(t) is the phase that slowly changes due to the slight deviation between the center frequency of the modulated wave and the local oscillation frequency. It is a term. The center frequency Wc/2π of the carrier wave is the symbol frequency 1/T
Since it is usually chosen to be much higher than , the phase term WcT can easily be set to 2π by adjusting the period T only slightly. Therefore, this term will be ignored below.

A signal γ B (t) obtained by inputting γ ₁ (t) and _{γ 3} (t) to the multiplication circuit 61 and a signal obtained by inputting γ ₂ (t) and γ ₄ (t) to the multiplication circuit 62 ζ ₄ (t) are given as follows.

γ ₁₃ (t)=γ ₁ (t)γ ₃ (t) = 1/2A(t-T) B ² cos [P(t-T)-P (t) +ΔQ(t-T)-ΔQ(t )+45°] +1/2A(t-T)B ² cos[P(t-T) +P(t)+ΔQ(t-T)+ΔQ(t)+45°]
...(6) γ ₂₄ (t)=γ ₂ (t)γ ₄ (t) = 1/2A(t-T)A(t)B ² cos [P(t-T) −P(t)+ΔQ (t-T)-ΔQ(t)+45°] -1/2A(t-T)A(t)B ² cos[P(t-T) +P(t)+ΔQ(t-T)+ΔQ(t) +45°〕
...(7) The signal γ _d1 (t) obtained by inputting γ ₁₃ (t) and γ ₂₄ (t) to the adder circuit 71 is as follows.

γ _d1 (t)=A(t-T)A(t)B ² cos [P(t-T) −P(t)+ΔQ(t-T)−ΔQ(t)+45°]
...(8) Similarly, γ ₁ (t) and γ ₄ (t) are input to the multiplier circuit 63, and γ ₂
(t) and γ ₃ (t) are input to the multiplier circuit 64 and the resulting signal is input to the subtraction circuit 72, so that the output signal γ _d2 (t) is as follows.

γ _d2 (t)=A(t-T)A(t)B ² sin [P(t-T) −P(t)+ΔQ(t-T)−ΔQ(t)+45°]
...(9) When the local oscillation frequency is approximately equal to the center frequency of the modulated wave, the phase term ΔQ(t-T)−ΔQ(t) is small and can be ignored. At this time, V _d1 (t)≒A(t-T)A(t)B ² cos [P(t-T)-P(t)+45°] ...(10) V _d2 (t)≒A( t-T)A(t)B ² sin [P(t-T)-P(t)+45°] ...(11) Since the delay time T is chosen to be equal to the symbol period, the phase term P(t-T)-P(t) varies as 0°, ±90°,
Since any point within 180° is taken, the phases of the signals V _d1 (t) and V _d2 (t) obtained by adding 45° to this point are as shown by the X mark in FIG. This causes the signal V _d1
(t) and V _d2 (t) by polarity determination circuits 81 and 8, respectively.
2 and obtained at the output terminals 91 and 92, the phase difference P(t-T)-P(t) is the fourth
It was found as shown in the figure, indicating that delayed detection was performed.

In this example, two sets of orthogonal signals of the local oscillator signal are used, namely a set of 0° and 90° and a set of 45° and
Although the phase difference between the 135° pairs was set to 45°, as is clear from Figure 3, even if the value is an odd multiple of 45°, the relationship shown in Figure 4 will only change.
Similarly, the detection output can be obtained. Also, this
In order to obtain a phase difference of an odd multiple of 45° or a 90° phase difference for in-phase and quadrature detection, instead of providing a phase difference between the local oscillation signals as in this example, the input modulated wave It is a well-known fact that a phase difference may be provided between signals.
Furthermore, it is obvious that two delay circuits 5 may be provided independently in the baseband band between the mixer 33 and the multiplier circuit 61 and between the mixer 34 and the multiplier circuit 62 instead of providing them in the high frequency band. moreover,
In the actual case where noise is present, the polarity determination circuit 8
Although it is necessary to sample the outputs of 1 and 82 at a time when the influence of noise is least, it is not related to the basic operation, so the explanation is omitted here.

As explained above, since the present invention can perform delayed detection using the direct conversion method, it has the effect of facilitating integration into an integrated circuit.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a diagram showing signal points of a four-phase phase modulated wave targeted by the present invention, and FIG. 3 is a diagram showing signal points for explaining the operation of the present invention. FIG. 4, which is a diagram showing points on a complex amplitude plane, is a diagram showing the relationship between two detected output signals and phase changes. In these figures, 1 is an input terminal, 2 is a local oscillator, 3 is a phase difference separation circuit, 31, 32,
33, 34 are mixers, 41, 42, 43, 44 are low-pass filters, 5 is a delay circuit, 61, 62,
63 and 64 are multiplication circuits, 71 is an addition circuit, 72 is a subtraction circuit, 81 and 82 are polarity determination circuits, 91 and 9
2 is a detection output terminal.

Claims (1)

[Claims] 1. A first quadrature detector which uses a four-phase phase modulated wave as an input signal and whose local oscillation signal is a signal obtained from the output of a local oscillator having an oscillation frequency approximately equal to the center frequency of the input modulated wave; a second quadrature detector whose relative phase differs by an odd multiple of 45°, the baseband signals of the first quadrature detector are used as first and second signals, and the output of the second quadrature detector is The baseband signals of the third and fourth
, the third and fourth signals have means for making the delays different from the first and second signals by the symbol period of the four-phase modulated wave, and the first A signal obtained by multiplying the signal by the third signal is defined as a fifth signal, a signal obtained by multiplying the second signal by the fourth signal is defined as a sixth signal, and a signal obtained by multiplying the signal by the fourth signal is defined as a sixth signal. A signal obtained by multiplying the signals of is set as a seventh signal, a signal obtained by multiplying the second signal and the third signal is set as an eighth signal,
A signal obtained by adding the fifth signal and the sixth signal is binarized, this is used as a first detection signal, and the seventh signal and the eighth signal are subtracted. A delay detection circuit characterized in that the obtained signal is binarized, this is used as a second detection signal, and a four-value signal obtained from a combination of the first and second detection signals is used as a detection output signal.