JP3129470B2 - DC current supply circuit - Google Patents

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 constituted by an IC or the like, the center frequency of the circuit is arbitrarily set by changing the constant current value of the circuit. At that time, a DC current supply circuit for supplying a constant current to these filters and trap circuits is provided.

As shown in FIG. 7, this type of DC current supply circuit comprises a current generating section 1 for generating a DC current and a current output section 2. The first transistor Q1 in the current generator 1 is supplied with a control voltage from the buffer 3 on its base and is always kept at a constant bias. The buffer 3 is an all-feedback buffer, and its (+) input terminal is supplied with a reference voltage from the reference voltage source 4, and its (-) input terminal is fed back with the emitter voltage of the first transistor Q1. The emitter of the first transistor Q1 is further connected to the volume VR via the terminal 5. The other end of this volume VR is connected to the ground potential point. The collector of the first transistor Q1 is connected to the collector of the second transistor Q2 and the base of the third transistor Q3. The emitter of the second transistor Q2 is connected to the power supply line 6 via the resistor R1. The third transistor Q3 has its collector grounded and its emitter connected to a resistor R.
2 to the power supply line 6 and the second
It is connected to the base of transistor Q2.

On the other hand, a current output unit 2 includes fourth, fifth, and sixth transistors Q4, Q5, Q6 connected as shown in FIG.
And resistors R3, R4, R5, and the currents I1, I5 from the collectors of the transistors Q4, Q5, Q6.
2, I3 are output. Transistors Q4, Q5, Q6
Constitutes a current mirror circuit together with the transistors Q2 and Q3 of the current generator 1, and outputs DC currents I1, I2 and I3 corresponding to the current Io flowing through the transistor Q1. These output DC currents I1, I2, I3
Also depends on the values of the resistors R3, R4 and R5. In FIG. 7, components other than the terminal 5 and the volume VR are formed in the IC, and the generated current Io is varied by operating the volume VR, whereby the output currents I1, I2, I3
To adjust the settings. Output currents I1, I2
I3 is supplied to a filter and a trap circuit in the same IC.

[0005]

In the above circuit,
The volume VR is an external component of the IC, and when mounted on a printed wiring board, may receive noise or interference from other circuits depending on the arrangement on the printed wiring board or the like. In particular, in a situation where a signal line is running nearby, the signal line is easily affected. Therefore, the DC current Io generated by the current generator 1
Swings in an alternating fashion. This swing is caused by the output currents I1, I2, I
3 means that the center frequency of a filter or a trap circuit to which I1, I2, and I3 are supplied fluctuates, and the frequency characteristics of those circuits deviate. In particular, in a semiconductor integrated circuit, interference may occur between an input terminal and a current adjustment terminal, and a capacitor cannot be added to the input terminal, causing a shift in a set frequency. Especially when the input terminal and the current adjustment terminal are separated, there is an effect of others, and the distance on the chip is limited,
It is difficult to prevent interference.

FIG. 8 shows the situation in that case, and it can be seen that the frequency characteristic has shifted from the set dotted line state to the solid line state. 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 to the trap circuit. Here, the higher the frequency, the larger the deviation is because the constant current is small in the high-pass filter. This is because it is larger than the rate of change of the supplied output current.

SUMMARY OF THE INVENTION An object of the present invention is to solve the problem that the output current changes due to the influence of the volume from other sources with a simple configuration.

[0008]

According to the present invention, a plurality of transistors constituting a current mirror circuit are provided.
Collector of transistor base and its one transistor
Through the first transistor for direct current value adjustment.
Connected to the attached volume, and the emitter of the first transistor
The voltage is compared with the reference voltage by the comparing means, and the comparison output
Is applied to the base of the first transistor.
The current mirror circuit is driven by the collector current of
The plurality of transistors
Power line connected to the collector of the
High frequency rejection capacitor between transistor collector
Has a configuration in which a.

[0009]

According to this configuration, since the AC fluctuation of the DC current received from the other through the adjusting volume is removed by the capacitor, the output DC current has no substantial effect.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1 embodying the present invention, the same parts as those of the conventional example shown in FIG. In the present embodiment, the capacitor C is provided between the collector of the first transistor Q1 and the power supply line 6 to remove the fluctuation (that is, the AC component) of the DC current Io due to noise, interference, or the like mixed in from the terminal 5. ing. Note that this capacitor C is also formed in the IC. Since the high frequency component is removed from the current Io by the capacitor C, the output currents I1, I2, I3
Does not include high frequency components. Therefore, when a circuit that uses these output currents is, for example, a trap circuit or the like, the advantage that their center frequencies do not deviate from the set value can be enjoyed. Therefore, there is no need to pay special attention to the arrangement of the volume VR and the like, 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 in the same IC. The integrated filter circuit 10 comprises one band pass filter 11 and two trap circuits 12 and 13. A signal (for example, an audio signal) supplied to an input terminal 16 is supplied to these band pass filters and It is led out to the output terminal 17 sequentially through the trap circuit. 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. FIG. 6 shows an overall frequency characteristic of the filter circuit 10.

Each of the band-pass filter 11 and the trap circuits 12, 13 is constituted by a circuit as shown in FIG. Here, 9 and 10 are conductance circuits using the dynamic resistance of transistors, and C1, C2 and C3 are capacitors. FIG. 4 shows a specific example of this circuit.
An output current I1, I2, or I3 from the current output unit 2 of the DC current supply circuit is supplied to a 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, As described above, since the output current is not affected by the others and maintains the set value set by the volume VR, the current flowing through the constant current sources Q11 and Q12 does not change after all, and the bandpass The set frequencies of the filter and the trap circuit do not change.

[0013]

As described above, according to the present invention, the AC swing of the DC current received from the other through the adjustment volume is reduced by the input transistor of the current mirror circuit.
Since it is removed by the capacitor provided between the collector and the power supply line , the output direct current has no substantial effect. Therefore, there is no need to pay special attention to the arrangement of the volume VR and the like, which is convenient for use.

[Brief description of the drawings]

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

FIG. 2 is a diagram showing a specific circuit using an output of the DC current supply circuit.

FIG. 3 is a diagram showing a basic circuit constituting the filter and the 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 the trap circuit in FIG. 2;

FIG. 6 is an overall frequency characteristic diagram of the bandpass filter and the trap circuit.

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]

 DESCRIPTION OF SYMBOLS 1 Current generation part 2 Current output part VR volume C capacitor

Claims (1)

(57) [Claims] A plurality of transistors constituting a current mirror circuit;
Base of transistor and collector of one of its transistors
And external for DC current value adjustment through the first transistor
And the emitter voltage of the first transistor.
The voltage is compared with the reference voltage by the comparing means, and the comparison output is
Applied to the base of the first transistor,
The current mirror circuit is driven by a collector current.
Power supply circuit connected to the collectors of the plurality of transistors.
Between the transistor and the collector of the one transistor
DC power supply having a capacitor for wave removal
Flow supply circuit.