JPH0447502B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field of the Invention The present invention relates to a carrier wave regeneration circuit that stably regenerates a carrier wave for synchronously detecting a PSK signal.

Prior Art and Problems Figure 1 is a block diagram of an example of a conventional carrier wave regeneration circuit that regenerates a carrier wave for synchronously detecting a 4-phase PSK signal. is a phase detector, 4 is a 90° phase shifter, 5 is a baseband processing circuit, 6 is a voltage controlled oscillator, 7
is a loop filter, and 7' shows another example of the loop filter. The output signal of the voltage controlled oscillator 6 is applied to the phase detector 3 via the phase detector 2 and the 90° phase shifter 4, the input 4-phase PSK signal is detected, and the detected output is added to the baseband processing circuit 5. It will be done. In the baseband processing circuit 5,
If the phase difference between the output signal of the voltage controlled oscillator 6 and the carrier wave component of the input 4-phase PSK signal is θ, then, for example, a signal of sin4θ is outputted, passed through the loop filter 7 as the control voltage of the voltage controlled oscillator 6, and the phase difference is The output signal phase of the voltage controlled oscillator 6 is controlled so that the phase difference θ becomes zero, and a carrier wave that is phase synchronized with the carrier wave component of the input 4-phase PSK signal is reproduced as the output signal of the voltage controlled oscillator 6. become.

As a loop filter for a carrier wave recovery circuit having such a phase-locked loop, a low-pass filter that combines a resistor and a capacitor is generally used. A filter may also be used.

Furthermore, the phase detection sensitivity of the phase detectors 2 and 3 and the voltage sensitivity of the voltage controlled oscillator 6 are not constant and vary depending on the product, and the phase detection sensitivity varies depending on the band limit of the transmission path. becomes.
Therefore, it is necessary to adjust various sensitivities for each product and depending on the conditions of use. Therefore, conventionally, for example,
A method for adjusting the level of the input PSK signal by connecting an attenuator to the input terminal 1, and a method for adjusting the loop gain by connecting an amplifier to the phase-locked loop were adopted. However, there are disadvantages in that the configuration is complicated and the variable range is narrow, and the amplifier requires a broadband configuration and is expensive. Also, when an active filter is used as a loop filter, it is possible to obtain a gain according to the ratio of the impedance on the input side of the operational amplifier and the feedback impedance, but in the configuration shown by 7', the DC gain becomes large. This has the drawback of causing problems with the stability of the phase-locked loop.

OBJECTS OF THE INVENTION It is an object of the present invention to make it possible to set a phase-locked loop gain with a simple configuration and to perform stable carrier wave reproduction. Examples will be described in detail below.

Embodiment of the invention FIG. 2 is a block diagram of an embodiment of the invention.
The same reference numerals as in FIG. 1 indicate the same parts. In the present invention, the loop filter 9 of the phase-locked loop includes an operational amplifier 10, a first resistor R1 on the input terminal side of the operational amplifier 10, and a second resistor connected in series for feedback.
, a resistor R2 and a capacitor C1, and a third resistor R3 connected in parallel to the capacitor C1. The gain of this loop filter 9 is expressed as R2+R3/R1, and
The AC gain can be prevented from becoming too large by selecting the third resistor R3 in parallel with the capacitor C1. Therefore, even when the first resistor R1 is adjusted to obtain a desired loop gain, the phase-locked loop can be operated stably.

FIG. 3 shows the essential loop filter of another embodiment of the present invention, in which the differential output signal of the amplifier 11 is passed through the first resistors R4 and R5 to the inverting input terminal of the operational amplifier 12 and The connection configuration is such that it is added to the non-inverting input terminal, and second and third resistors R6 and R7 and a capacitor C2 are used for feedback of the operational amplifier 12.
This is a connection between Like the previous embodiment, the loop filter of this embodiment can arbitrarily adjust the loop gain without destabilizing the operation of the phase-locked loop, and also outputs a differential output signal to the operational amplifier 12. By inputting
This has the advantage that drift can be reduced.

Effects of the Invention As explained above, the present invention applies a control voltage corresponding to the phase difference between the carrier wave of the PSK signal and the recovered carrier wave to the voltage controlled oscillator 6 that outputs the recovered carrier wave for synchronously detecting the received PSK signal. The loop filter 9 to be added is replaced by high gain operational amplifiers 10 and 12.
, first resistors R1 and R4 for loop gain adjustment on the input side, and a second resistor R connected in series between the output terminal and input terminal of the operational amplifiers 10 and 12.
2. R6, capacitors C1 and C2, and a third resistor R connected in parallel to these capacitors C1 and C2.
3, R7, the AC gain will not become extremely large due to the third resistor R3, R7, and even if the loop gain is adjusted by adjusting the first resistor R1, R6, the phase synchronization will be maintained. The operation of the loop can be stabilized.

Therefore, when adjusting the phase-locked loop gain including the voltage-controlled oscillator 6 that outputs the recovered carrier wave in response to variations in the sensitivity of the phase detectors 2 and 3 that synchronously detect PSK signals and the voltage-controlled oscillator 6,
Since the AC gain can also be set to an appropriate value,
There is an advantage that stable carrier wave regeneration can be performed.

[Brief explanation of the drawing]

Figure 1 is a block diagram of a conventional carrier wave regeneration circuit.
FIG. 2 is a block diagram of one embodiment of the present invention, and FIG. 3 is a block diagram of essential parts of another embodiment of the present invention. 1 is input terminal, 2 and 3 are phase detectors, 4 is 90°
phase shifter, 5 is a baseband processing circuit, 6 is a voltage controlled oscillator, 7, 7', 9 are loop filters, 10,
12 is an operational amplifier, 11 is a differential output amplifier, R
1 to R7 are resistors, and C1 and C2 are capacitors.

Claims (1)

[Claims] 1. A regenerated carrier wave for synchronously detecting a PSK signal is output from a voltage controlled oscillator, a phase difference between the carrier wave of the PSK signal and the regenerated carrier wave is detected by a baseband processing circuit, and the phase difference is detected by a baseband processing circuit. In the carrier wave regeneration circuit which outputs the control voltage of the voltage controlled oscillator through a loop filter, a signal corresponding to the voltage controlled oscillator is used as the control voltage of the voltage controlled oscillator. A first resistor for loop gain adjustment on the input side of the amplifier, a second resistor and a capacitor connected in series between the output terminal and the input terminal of the operational amplifier, and a third resistor and a capacitor connected in parallel to the capacitor. A carrier wave regeneration circuit comprising a resistor.