JPS59191906A - Phase detecting circuit - Google Patents

Abstract

PURPOSE:To obtain a phase detecting circuit which increases extremely only the phase detection gain when the signal of a specific phase relation is supplied, by feeding the output voltage of one side of the phase detecting circuit back to a current source circuit after smoothing the output voltage and controlling the current value of said current source circuit. CONSTITUTION:The voltage of an output terminal 13 rises up when the signal having a certain phase difference is supplied to input terminals 14 and 15 respectively. Under such conditions, the voltage of an output terminal 12 drops. Then the voltage of a voltage source 33 is compared with the voltage of the terminal 12 by a feedback circuit consisting of transistors (TR) 28-31. Thus the collector current of a TR7 is reduced, and therefore the mutual conductance between TRs 5 and 6 is reduced. As a result, the phase detection gain is lowered. On the contrary, the voltage of the terminal 12 rises up when the signal having a phase relation in the direction where the voltage of the terminal 13 is reduced. Thus the collector current of the TR7 is increased to increase the mutual conductance between the TRs 5 and 6. Thus, the phase detection gain is increased.

Description

[Detailed description of the invention] [Field of application of the invention] FIG. 1 shows a conventional fully balanced phase detection circuit.

However, in order to explain the basic operation, the low-pass filter is not shown. The conventional fully balanced phase detection circuit will be explained below with reference to FIG. transistor 7
is a current source, and its current value is determined by the voltage source 10 and the resistor 26, which are connected via the resistor 22. transistor 5
．． Reference numeral 6 constitutes a differential circuit to which a bias is applied from a voltage source 9 through resistors 20 and 21 and is dependent on a current source circuit formed by a transistor 7. Transistors 1 to 4 are biased by voltage source 8 through resistors 18 and 19, and are dependent on the output of the differential circuit constituted by transistors 5 and 6, thereby forming a differential circuit. transistor 1
Resistors 16 and 47 connected between ~4 and power supply terminal 11
is a load resistance of a fully balanced circuit constituted by a differential circuit constituted by transistors 5 and 6 and a differential circuit constituted by transistors 1 to 4. 12 and 13 are output terminals, which are connected to resistors 16 and 17 and transistors 1 to 1.
4 connection points. Reference numerals 14 and 15 are input terminals, which provide signals through coupling capacitors 24 and 25 to respective differential circuits constituted by transistors 1 to 4 and 5 and 6. Although any waveform of the signal applied to the input terminals 14 and 15 may be used, in order to explain the operation, it is assumed here that a square wave is input. Transistor 1~
4 acts as a switch according to the square wave input to the input terminal 14, and when the square wave input to the input terminal 14 is at the 'E' level, the transistor 1.4 becomes 0.N, and the transistors 2 and 6 become oI4'F. When the level is L, transistors 2 and 3 are ON, and transistor 1.4 is U/”F.
becomes. Here, the phase difference between the two input signals is 0', 9
Output terminal 16 in six states of 0' and 180'
The output voltage waveform that appears is shown in FIG. 10 in Figure 2
1 is a voltage waveform applied to the input terminal 14, 102 is a voltage waveform applied to the input terminal 15, and 103 is a voltage waveform appearing at the output terminal 15. Then, when the two input signals are in phase, (AI is 90'), and when they have a phase difference, (cl is 12o).

This is when the phase difference is . By supplying the output voltage appearing at the output terminal 13 to the low-pass filter, a phase detection output is obtained as an average DC voltage at the output of the low-pass filter. The phase detection characteristic of this phase detection circuit is shown in FIG. 3. The slope of the phase detection characteristic is called the detection gain, and is constant with respect to the phase relationship of the input signal. In the phase detection circuit having the circuit configuration shown in FIG. 1, the phase detection gain must also be reduced as the power supply voltage decreases.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a phase detection circuit that greatly increases only the phase detection output when a signal with a specific phase relationship is input.

[Summary of the invention]

In order to achieve the above object, in the present invention, in a phase detection circuit having a fully balanced differential amplifier circuit configuration, which is equipped with a current source circuit, the output voltage of one of the two outputs of the phase detection circuit is smoothed. The present invention is characterized in that the obtained phase detection output information is fed back to the current source circuit to control the current value.

[Embodiments of the invention]

FIG. 4 shows a phase detection circuit which is an embodiment of the present invention. Components in FIG. 4 that are the same as those in FIG. 1 are given the same numbers. The present invention will be explained below using FIG. 4. Capacitors 26 and 27 are connected to both ends of the resistors 16 and 17, respectively, and a transistor 28 and a resistor 35 forming a low-pass filter form an emitter follower and perform impedance conversion. The transistor 29, the voltage source 52, and the resistors 34 and 37 constitute a constant current source to determine the total emitter current of the differential amplifier circuit constituted by the transistors 30 and 31. In the differential amplifier circuit composed of transistors 30 and 31, the voltage source and the resistor 36 apply bias to one transistor 30 constituting the differential amplifier circuit, and at the same time act as a reference voltage. The voltage applied to the base of the transistor 31 is compared with the voltage applied to the base of the transistor 31 as a reference, and the error of this comparison result can be obtained as an output. The output of output terminal 12 is applied to the base of transistor 310 through an emitter follower formed by transistor 28. therefore,
Transistor! In the differential amplifier formed by IO, 31,
A comparison is made between the reference voltage source 33 and the output of the output terminal 12. The output of this differential amplifier is applied to the base of transistor 7. Transistor 7 is transistor 56
This current is controlled by a differential amplifier formed by transistors 30 and 31. This control means that the polarity of the signal from the output terminal 12 to the base of the transistor 70 is positive, and the polarity is reversed from the base of the transistor 70 to the collector. Since it is subordinate to transistor 7,
The polarity from the collector of the transistor 7 to the output terminals 12 and 13 is positive, and the overall feedback loop constitutes a negative feedback circuit. Now, suppose that the voltage at the output terminal 13 has increased by inputting signals with a certain phase difference to the input terminals 14 and 15, then the output terminal 12 will output an output complementary to the output from the output terminal 16. is about to occur. Therefore, the voltage at the output terminal 12 tends to drop, but the feedback circuit formed by the transistors 28 to 31 causes the voltage at the voltage source 33 to drop.
By comparing the voltage at the output terminal 12 and the voltage at the output terminal 12, the collector current of the transistor 7 is reduced. transistor 7
By reducing the collector current of transistor 5.
Oh no! Since I- (mutual conductance) decreases, the phase detection output decreases. Conversely, when a signal with a phase relationship in the direction that the voltage at the output terminal 16 decreases is input, the voltage at the output terminal 12 tends to increase, but the feedback circuit composed of transistors 28 to 31 prevents the voltage from increasing. source 6
3 and the voltage at the output terminal 12, the collector current of the transistor 7 increases. As the collector current of transistor 7 increases, transistor 5
, 609'' increases, the 1-phase detection gain increases.

As described above, by comparing the voltage at the output terminal 12 and the voltage at the voltage 33 and controlling the current of the transistor 7, the phase detection characteristic is determined as shown in Fig. 5 when a signal with a certain phase difference is input. 1, the phase detection gain becomes larger than that shown in FIG. On the other hand, when a signal whose phase is shifted by 180 degrees from that phase is input, the detection sensitivity becomes smaller than that shown in FIG.

Next, a specific usage example showing the effectiveness of the present invention will be described. FIG. 6 is a block diagram showing one example of the 501
is the 1B delay line, 602 is the phase detection circuit, 303
is a voltage controlled amplifier, 304° is a threshold circuit, 6
05 is an input terminal, and 506 is an output terminal. This circuit identifies the signal input to the input terminal 605 by comparing the phase with that 1H before.

The amplification degree of the amplifier 303 is switched only when the phase relationship is , and the output level of the signal is specially controlled.
In this case, the phase detection circuit of the present invention can more easily detect a specific phase relationship. Therefore, the amplification degree of the amplifier can be switched accurately. Note that the specific phase relationship can be adjusted to any phase shift relationship by arranging a phase shift circuit in front of the input terminals 14 and 15 in FIG. 4 and appropriately setting the amount of shift. [Effect] According to the present invention, it is possible to extremely increase the phase detection gain only when an input signal has a specific phase relationship. Therefore, only signals with a specific phase relationship can be reliably detected.

Also, recently, in order to save power in electronic circuits, there is a tendency to set the power supply voltage of the circuit low, but in the circuit configuration shown in Figure 1, the phase detection gain has to be lowered as the power supply voltage decreases. However, in the case of FIG. 4, the phase detection gain can be kept sufficiently high under a specific phase relationship.

[Brief Description of the Drawings] Fig. 1 is a diagram of a conventional phase detection circuit, Fig. 2 is a waveform diagram showing an example of the waveform of the output terminal 16 with respect to the phase difference of input signals, and Fig. 6 is a diagram of the conventional phase detection circuit. Phase detection characteristic diagram of the phase detection circuit of
FIG. 4 is a circuit diagram showing one embodiment of the phase detection circuit of the present invention, FIG. 5 is a phase detection characteristic diagram of one embodiment of the phase detection circuit of the present invention, and FIG. 6 is a circuit diagram showing an embodiment of the phase detection circuit of the present invention. FIG. 1~7.28-51-・) La7 register, B510.3
25'5...Power, power supply, 11...Power terminal, 12
, 15 mountain output terminal・, 14 , 15...input terminal,
16-25, 54, 57...Resistance, 24-27.
...Capacitor, 6o1...1B delay line, 3
02... Phase detection circuit, 303... Voltage controlled amplifier, 504... Threshold circuit, 3o5... Input terminal, 606... Output terminal. Rod l Figure/l Stem 3 Figure Sheep + Fertilizer

Claims (1)

[Claims] 1 Consists of a current source circuit, a first differential circuit dependent on the current source circuit, and a second differential circuit dependent on the output of the first differential circuit, and In a phase detection circuit in which the differential circuit is configured in a fully balanced type, average output voltage information at one output terminal of the two outputs of the phase detection circuit is fed back to the current source circuit, and the current source circuit A phase detection circuit characterized by controlling a current value of.