JPH0330341B2 - - Google Patents

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a quadrature detector used in a polyphase phase modulation method or a quadrature multi-level amplitude modulation method, and in particular to an automatic gain control ( (hereinafter referred to as "AGC") technology improvement.

[Conventional technology]

As shown in Figure 1, conventional AGC methods often detect the signal level in the intermediate frequency (hereinafter referred to as "IF") band and use the output to control a variable attenuator in the IF band. Are known. 1 in Figure 1
is an amplifier with an IF band variable attenuator, 2 is a DC amplifier,
3 indicates an IF section level detector.

[Problem that the invention seeks to solve]

Generally, when the modulation method becomes multiphase or multivalued, a more accurate AGC function is required of the transmission system. However, since the conventional method performs level detection in the IF band, it is not possible to compensate for gain fluctuations in the detection circuit or baseband circuit that follows the IF band. Furthermore, since it is an IF band circuit, consideration must be given to level distribution, impedance deterioration, etc., and it has drawbacks such as difficulty in adjustment.

The present invention improves this point, and aims to provide a quadrature detector using a stable and economical AGC method suitable for a multiphase phase modulation method or a quadrature multilevel amplitude modulation method.

[Means for solving problems]

In general, in polyphase phase modulation or orthogonal multilevel amplitude modulation, synchronous detection is performed on the receiving side using recovered carrier waves whose phases differ from each other by π/2. Since the two output signals thus detected have multiple values, a full-wave rectifier circuit is often used in consideration of ease of signal processing and economic efficiency of the circuit.

The present invention is characterized in that the reception level is detected by combining the outputs of the full-wave rectifier circuits with a phase shift of π/2, and an AGC loop is constructed.

The quadrature detector of the present invention includes a branching means for branching an intermediate frequency signal obtained as a reception output into two, an oscillation means for outputting a reproduced intermediate frequency carrier wave, and a phase shift of the reproduced intermediate frequency carrier wave by π/2. phase shifting means; and phase detection means for obtaining two baseband detection signals having phases different from each other by π/2 from the intermediate frequency signal branched into two, the output of the oscillation means, and the output of the phase shifting means. , full-wave rectifying means for full-wave rectifying these two baseband signals, combining means for combining and averaging the respective outputs of the full-wave rectifying means, and generating the intermediate frequency signal in response to the output of the combining means. Alternatively, the present invention is characterized by comprising: level control means for controlling the level of the baseband detection signal; and means for controlling the oscillation phase of the oscillation means using the output of the full-wave rectification means.

〔Example〕

An embodiment of the present invention will be described based on the drawings.

FIG. 2 is a circuit diagram of a main part of an embodiment of the apparatus of the present invention.

IF band variable attenuator amplifier 1 receiving IF input
The output of the signal branching circuit 4 is led to the signal branching circuit 4. The output branched by this signal branching circuit 4 is sent to a phase detector 5.
and 5' respectively. The output of the π/2 phase shifter 6 is guided to the phase detector 5. The outputs of the phase detectors 5 and 5' are guided to full-wave rectifiers 7 and 7', respectively.
The outputs of the full-wave rectifiers 7 and 7' and the phase detectors 5 and 5' are led to a received data regeneration circuit 8.

Furthermore, the outputs of these full-wave rectifiers 7 and 7' are
The signal is guided to a signal synthesis circuit 9. The output of this signal synthesis circuit 9 is led to a DC amplifier 2. The output of this DC amplifier 2 is led to the control input of the IF band variable attenuator equipped amplifier 1. Further, the outputs of the full-wave rectifiers 7 and 7' are led to an automatic phase control signal generation circuit 10. The output of this automatic phase control signal generation circuit 10 is guided to a low frequency converter 11. The output of this low frequency generator 11 is guided to a voltage controlled oscillator 12. The output of this voltage controlled oscillator 12 is guided to the π/2 phase shifter 6 and the phase detector 5', respectively.

FIG. 3 is an operation time chart showing the signal waveforms indicated by the x marks in FIG. 2. In FIG. 3, the ○ marks indicate the pull-in points of orthogonal amplitude modulation, and the ○× points indicate the 8-phase pull-in points.

Next, the operation of the gain control circuit of this embodiment will be explained with reference to FIG.

The received input IF signal is amplified to a specified level by the variable attenuator equipped amplifier 1 and input to the signal branch circuit 4 . The output of the signal branching circuit 4 is input to phase detectors 5 and 5' for quadrature phase detection,
The input signal is phase-detected using the output signal of the voltage-controlled oscillator 12 and a signal obtained by delaying the output signal of the voltage-controlled oscillator 12 by π/2 with phase shift 6 as a reference carrier signal. The phase-detected output signals become baseband signals a and b. This baseband detected waveform signal a leads the detected waveform b by π/2 in phase. This is because the phase shifter 6 delays the phase of the reference carrier wave supplied from the voltage controlled oscillator 12 by π/2, so that the output detected waveform becomes a waveform advanced by π/2.

Baseband signals a and b are input to full-wave rectifiers 7 and 7' and are full-wave rectified into signal waveforms c and d. These outputs c and d are synthesized by the signal synthesis circuit 9 into a waveform shown in FIG. 3e. The output waveform shown in e is amplified by the DC amplifier 2, fed back to the variable attenuator equipped amplifier 1, and controlled to keep the signal level constant at the time of signal processing. This performs gain control including compensation for gain fluctuations in the internal circuit.

On the other hand, the full-wave rectified signals c and d are input to an automatic phase control signal (APC) generation circuit 10, passed through a low-pass filter 11, and supplied to a voltage controlled oscillator 12 as an APC signal. Generate a reference carrier signal.

Generally, in an orthogonal modulation system, two orthogonally detected output levels are equal. However, in a polyphase phase modulation system, for example, an eight-phase phase modulation system, two output levels subjected to quadrature detection are different at the same time slot. However, as shown in FIG. 3, even in the phase modulation method of 8 phases or less and the quadrature amplitude modulation method, the output e remains unchanged in the normal pull-in phase, and does not change significantly even with the phase shift of the reproduced carrier wave.
In other words, there is no adverse effect on the pull-in process of the reproduced carrier wave.

Even with polyphase modulation of 16 or more phases, the present invention can be implemented in the same way by inserting a smoothing circuit into the circuit for the output signal e.

In addition, in the above example, by shifting the phase of the local oscillation signal supplied to one of the two phase detection circuits by π/2, the phases of the outputs of the two phase detection circuits are made to differ by π/2. However, by applying local oscillation signals of the same phase or other phase relationships to two phase detection circuits, and changing the phase of the signal at the input or output of each phase detection circuit, it is possible to change the phase by π/2. Signals having different phases can be obtained, and the present invention can be similarly implemented using these signals.

Furthermore, the present invention can be similarly implemented with respect to multi-value signals of three or more values.

〔Effect of the invention〕

As explained above, according to the present invention, outputs of detection circuits whose phases differ by π/2 phase are combined.
We decided to apply AGC by monitoring the overall gain fluctuations of the IF section circuit, the detection section circuit, the following baseband circuit, etc. at the time of signal processing. Therefore, AGC at the stage of conventional intermediate frequency signals
Compared to the above, it is possible to construct a demodulation device that is extremely stable against external level fluctuations and internal circuit gain fluctuations without providing any new control circuit. Furthermore, a variable attenuator for AGC can be placed in both the IF band and the baseband band. Furthermore, according to the present invention, stability against temperature fluctuations or external power supply voltage fluctuations can also be increased.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of the main parts of a conventional device. FIG. 2 is a block diagram of essential parts of an embodiment of the apparatus of the present invention. FIG. 3 is an operation time chart showing the signal waveforms at the points marked with x marks in FIG. 2. 1...Amplifier with IF band variable attenuator, 2...DC amplifier, 3...IF section level detector, 4...Signal branch circuit, 5, 5'...Phase detector, 6...π/
2 phase shifter, 7, 7'...Full wave rectifier, 8...
Received data regeneration circuit, 9... Signal synthesis circuit, 10
. . . automatic phase control signal generation circuit, 11 . . . low frequency generator, 12 . . . voltage controlled oscillator.

Claims (1)

[Claims] 1. Branching means for branching an intermediate frequency signal obtained as a received output into two, oscillation means for outputting a reproduced intermediate frequency carrier wave, and a phase shifter for shifting the phase of the reproduced intermediate frequency carrier wave by π/2. a transition means; a phase detection means for obtaining two baseband detection signals having phases different from each other by π/2 from the intermediate frequency signal branched into the two, the output of the oscillation means, and the output of the phase shift means; full-wave rectifying means for full-wave rectifying each of these two baseband signals; a combining means for combining and averaging the respective outputs of the full-wave rectifying means; A quadrature detector comprising: level control means for controlling the level of a baseband detection signal; and means for controlling an oscillation phase of the oscillation means using the output of the full-wave rectification means.