JPH04328614A - Direct current supplying circuit - Google Patents

Abstract

PURPOSE:To give no influence to a DC current outputted from a current output part by eliminating the AC fluctuation of the direct current supplied via an adjusting volume with the use of a capacitor provided on a current generating part. CONSTITUTION:A capacitor C is provided between the collector the 1st transistor Q1 and the power line 6 of a current generating part 1 which generates a direct current. The capacitor C eliminates the fluctuation of the direct current, i.e., the AC component caused by the noises mixed through a terminal 5, the interference, etc. Thus the high frequency components are never included in the output currents 11-13 since these components are eliminated by the capacitor C. Therefore when the output current is used by a trap circuit, for example, the center frequency of the trap circuit is always coincident with a set level. Then no special consideration is needed for the arrangement of a volume VR which adjusts the DC value. Then the availability of a direct current supply circuit is attained.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a DC current supply circuit, and more particularly to a DC current supply circuit having a volume for adjusting and setting a current value.

0002

2. Description of the Related Art For example, when a filter or a trap circuit is constructed using an IC or the like, the center frequency of these circuits can be arbitrarily set by varying the constant current value of those circuits. At that time, a DC current supply circuit is provided to supply a constant current to these filters and trap circuits.

As shown in FIG. 7, this type of DC current supply circuit consists of a current generation section 1 that generates a DC current and a current output section 2. The first transistor Q1 in the current generating section 1 is supplied with a control voltage from the buffer 3 to its base so that it is always maintained at a constant bias. Buffer 3 is a full feedback type buffer, and its (+
) A reference voltage from a reference voltage source 4 is applied to the input terminal,
The emitter voltage of the first transistor Q1 is fed back to the (-) input terminal. The emitter of the first transistor Q1 is further connected to the volume VR via the terminal 5. The other end of the volume VR is connected to a ground potential point. Also,
The collector of the first transistor Q1 is connected to the second transistor Q.
2 and the base of the third transistor Q3. The emitter of the second transistor Q2 is the resistor R1
It is connected to the power supply line 6 via. The third transistor Q3 has its collector grounded, and its emitter connected to the power supply line 6 via a resistor R2 and to the base of the second transistor Q2.

On the other hand, the current output section 2 includes fourth, fifth, and sixth transistors Q4, Q5, and Q6 connected as shown in the figure, and resistors R3, R4, and R5. , Q6 currents I1, I2,
I3 is output. Transistors Q4, Q5, and Q6 constitute a current mirror circuit together with transistors Q2 and Q3 of current generating section 1, and output direct currents I1, I2, and I3 corresponding to current Io flowing through transistor Q1. Note that the values of these output DC currents I1, I2, and I3 also depend on the values of resistors R3, R4, and R5. In FIG. 7, everything except the terminal 5 and the volume VR is formed inside the IC, and by operating the volume VR, the generated current Io
The output currents I1, I2, and I3 are adjusted and set accordingly. Output current I1, I2, I3
is supplied to a filter, a trap circuit, etc. within the same IC.

[0005]

[Problem to be solved by the invention] In the above circuit,
The volume VR is an external component of an IC, and when it is mounted on a printed wiring board, it may receive noise or interference from other circuits depending on its arrangement on the printed wiring board. Particularly in situations where a signal line runs nearby, it is easy to be influenced by the signal line. Therefore, the DC current Io generated by the current generation unit 1 fluctuates in an AC manner. This swing is the output current I1, I2, I3
This means that the center frequencies of filters, trap circuits, etc. to which I1, I2, and I3 are supplied will vary, causing a problem that the frequency characteristics of these circuits will deviate. Particularly in semiconductor integrated circuits, there may be interference between the input terminal and the current adjustment terminal, making it impossible to add a capacitor to the input terminal, causing a deviation in the set frequency. Particularly when separating the input terminal and current adjustment terminal, there are influences from other terminals, and there is also a limit to the distance on the chip, making it difficult to prevent interference.

FIG. 8 shows the situation in this case, and it can be seen that the frequency characteristics have shifted from the set state shown by the dotted line to the state shown by the solid line. Incidentally, FIG. 8 shows the overall characteristics when one of the three output currents in FIG. 7 is applied to the band pass filter and two output currents are applied to the trap circuit. Here, the deviation is especially large at higher frequencies because the constant current is small in the high-frequency filter, so the ratio of change in the output current applied to the high-frequency circuit to the change in the generated current Io is greater than that in the low-frequency circuit. This is because it is large compared to the rate of change in the supplied output current.

It is an object of the present invention to solve the above-mentioned problem that the output current changes due to the influence of other factors on the volume with a simple configuration.

[0008]

[Means for Solving the Problems] In order to achieve the above object, the present invention includes a current generating section that generates a direct current, and a current output that outputs a direct current corresponding to the direct current generated by the current generating section. a volume provided in the current generation unit for adjusting and setting the generated DC current value;
In the DC current supply circuit consisting of the following, a capacitor for removing high frequency components is provided in the current generating section.

[0009]

[Operation] According to this structure, since the alternating current fluctuations received from other sources via the adjustment volume are removed by the capacitor, there is no substantial effect on the output direct current.

0010

DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1 in which the present invention is implemented, parts that are the same as those in the conventional example shown in FIG. In this embodiment, by providing a capacitor C between the collector of the first transistor Q1 and the power supply line 6, fluctuations in the DC current Io (i.e., AC components) due to noise or interference introduced from the terminal 5 are removed. ing. It is assumed that this capacitor C is also formed within the IC. In this way, the high frequency components are removed from the current Io by the capacitor C, so the output currents I1, I2, I3
does not include high frequency components. Therefore, if the circuit using these output currents is, for example, a trap circuit, it is possible to enjoy the advantage that the center frequency thereof will not deviate from the set value. Therefore, there is no need to pay special consideration to the arrangement of the volume VR, which is convenient for use.

FIG. 2 shows an embodiment in which the output currents I1 to I3 of the DC current supply circuit of FIG. 1 are supplied to an integrated filter circuit 10 formed within the same IC. This integrated filter circuit 10 consists of one bandpass filter 11 and two trap circuits 12 and 13, and a signal (for example, an audio signal) applied to an input terminal 16 is transmitted through these bandpass filters and two trap circuits 12 and 13. It passes sequentially through the trap circuit and is led out to the output terminal 17. The frequency characteristics of the bandpass filter 11 constituting the integrated filter circuit 10 are shown in FIG. 5B, and the frequency characteristics of the trap circuits 12 and 13 are shown in FIGS. 5A and 5C, respectively. The overall frequency characteristics of the filter circuit 10 are shown in FIG.

The bandpass filter 11 and the trap circuits 12 and 13 are both constructed of circuits as shown in FIG. Here, 9 and 10 are conductance circuits that utilize the dynamic resistance of transistors, and C1, C2, and C3 are capacitors. FIG. 4 shows a concrete example of this circuit. An output current I1, I2, or I3 from the current output section 2 of the DC current supply circuit is applied to the terminal 21 in FIG. The current flowing through the constant current sources Q11 and Q12 for the differential transistors constituting the dynamic resistance portions 22 and 23 is determined by the DC current supplied to the terminal 21, but according to the DC current supply circuit of this embodiment, the As mentioned above, the output current is not influenced by anything else and maintains the set value set by the volume VR, so the current flowing through the constant current sources Q11 and Q12 does not change, resulting in bandpass. The set frequencies of the filter and trap circuits will not change.

[0013]

Effects of the Invention As explained above, according to the present invention, the alternating current fluctuations of the direct current received from other sources via the adjustment volume are removed by the capacitor provided in the current generating section, so that the current output is reduced. There is no substantial effect on the direct current output from the section. Therefore, there is no need to pay special consideration to the arrangement of the volume VR, which is convenient for use.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing a direct current supply circuit embodying the present invention.

FIG. 2 is a diagram showing a specific circuit that uses the output of the DC current supply circuit.

FIG. 3 is a diagram showing a basic circuit configuring the filter and trap circuit of FIG. 2;

FIG. 4 is a circuit diagram showing a specific example of FIG. 3;

FIG. 5 is a frequency characteristic diagram of the bandpass filter and trap circuit in FIG. 2;

FIG. 6 is a comprehensive frequency characteristic diagram of those bandpass filters and trap circuits.

FIG. 7 is a circuit diagram of a conventional example.

FIG. 8 is a characteristic diagram of a circuit using a conventional example.

[Explanation of symbols]

1 Current generation section 2 Current output section VR volume C Capacitor

Claims (1)

[Claims] 1. A current generating section that generates a direct current, a current output section that outputs a direct current according to the direct current generated by the current generating section, and a current generating section that is provided in the current generating section and generates the generated direct current. 1. A DC current supply circuit comprising a volume for adjusting and setting a current value, wherein the current generating section is provided with a capacitor for removing high frequency components.