JPH05129941A - Phase comparator - Google Patents

Abstract

PURPOSE:To reduce the number of pins of a bipolar semiconductor integrated circuit by forming a switching circuit with a diode bridge composed of 4 diodes and two constant current sources so as to eliminate the need for an externally fitted MOS transistor(TR). CONSTITUTION:When a current flows to constant current sources 20, 21 a phase comparison output current from the output terminal 6 of a computing element 1 flows to a sample-hold capacitor 16 from an output terminal 18 via a diode bridge switching circuit composed of diodes 22-25. On the other hand, when no current flows to the constant current sources 20, 21, the switching circuit is opened and a voltage across the capacitor 16 is held. Thus, the switching circuit is formed by the diode bridge to eliminate the need for an expensive externally fitted MOS, TR, thereby decreasing the number of pins of the bipolar semiconductor integrated circuit.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a phase comparator used in a PLL circuit or the like.

[0002]

2. Description of the Related Art A description will be given with reference to FIG. The arithmetic unit 1 includes three differential amplifiers 8 to 10 and three current mirrors 11 to 1
In the multiplier composed of 3 and the current source 7 having the current value I ₁ , the phase difference between the two signals at the input terminals 4 and 5 is converted to the phase comparison output current ie at the output terminal 6. Reference numeral 2 denotes a current switch circuit, which is composed of a MOS transistor 14 and conducts between the source and the drain only when the voltage of the gate 15 is higher than the threshold voltage, and the phase comparison output current ie charges the hold capacitor 16 in the subsequent stage. To discharge. Then, when the voltage of the gate 15 is lower than the threshold voltage, the MOS transistor 14 is cut off, and the output current of the arithmetic unit 1 becomes equal to the hold capacitor 16
Is not transmitted to the hold capacitor 16 and the terminal voltage of the hold capacitor 16 is held. This terminal voltage is transmitted to the VCO control terminal 18 to control the VCO oscillation frequency of the VCO circuit 19.

[0003]

When such a circuit is to be made into a bipolar semiconductor integrated circuit, it is bidirectional (acts on both the charging direction and the discharging direction with respect to the capacitor 16).
The current switch circuit of 1 used a MOS transistor as an external component. Then, it is necessary to separately provide the phase comparison output terminal 6 and the VOC oscillation frequency control terminal 18 in the bipolar semiconductor integrated circuit, which causes a problem that the number of pins of the bipolar semiconductor integrated circuit increases.
Further, there is a problem that an expensive MOS transistor is required as an external component.

The present invention solves the above problems, and an object thereof is to provide a bipolar semiconductor integrated circuit phase comparator having a small number of pins.

[0005]

In order to achieve the above object, the present invention has a structure including a diode bridge formed of four diodes and two constant current sources.

[0006]

With the above structure, expensive MOS transistors are not required as external parts.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A phase comparator according to an embodiment of the present invention will be described below with reference to FIG.
Will be described with reference to.

Elements having the same functions as those in FIG. 2 are designated by the same reference numerals. When the currents of the constant current sources 20 and 21 are I ₀ , the phase comparison output current ie from the output terminal 6 of the arithmetic unit 1
Is a balanced bridge circuit composed of diodes 22 to 25.
It flows to 6. The same applies when discharging from the capacitor 16. On the other hand, when no current flows in the constant current sources 20 and 21, the diode bridge switch circuit is in an open state and the terminal voltage of the capacitor 16 is held.
In this way, the phase comparison output current of the arithmetic unit is transmitted to the hold capacitor 16 in the subsequent stage while the current is flowing through the constant current sources 20 and 21, and the current is not flowing through the constant current sources 20 and 21 during the period. The terminal voltage of the hold capacitor 16 can be held.

As described above, according to the phase comparator of the embodiment of the present invention, since the switch circuit is constituted by the diode bridge instead of the MOS transistor, the external MOS is provided.
Since the transistor is unnecessary, the number of pins can be reduced even when the bipolar semiconductor integrated circuit is used.

[0010]

As is apparent from the above-described embodiments, according to the present invention, the current switch for transmitting the phase comparison output current of the arithmetic unit to the hold capacitor in the subsequent stage only for a predetermined period and holding it for the other period is a MOS transistor. Since it can be realized without using a bipolar semiconductor integrated circuit, an expensive MOS transistor is not required as an external component,
Further, when the MOS transistor was used as an external component as the number of pins of the semiconductor integrated circuit, two pins were required. However, since the constant current sources 20 and 21 can be realized by the bipolar semiconductor integrated circuit, the VCO control terminal 18 has We can provide a phase comparator that requires only one pin.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a phase comparator and a VCO circuit according to an embodiment of the present invention.

FIG. 2 is a circuit diagram showing a conventional phase comparator and VCO circuit.

[Explanation of symbols]

 1 calculator (multiplier) 16 hold capacitor 20,21 current source 22,23,24,25 diode

Claims (1)

[Claims] 1. A multiplier, a diode bridge switch circuit connected between a phase comparison output current terminal of the multiplier and a hold capacitor, and a current source for supplying a constant current to the diode bridge switch circuit. A phase comparator in which the current source supplies a constant current and cuts off the constant current during other periods.