JPH0347768B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a bias power supply circuit, and more particularly to reducing noise in a bias power supply circuit installed inside a semiconductor integrated circuit device.

FIG. 1 shows a bias power supply section of a conventional semiconductor integrated circuit device. In such a semiconductor integrated circuit device 2, a constant current source 4 is installed inside the device,
A series circuit of a diode 6 and a resistor 8 is connected to this constant current source 4, and a terminal 10 is formed at the connection point.
A bypass capacitor 12 is connected between this terminal 10 and a ground point.

The portion where the terminal 10 is formed becomes the output point of the bias power supply circuit inside the integrated circuit device 2, and the bias output is sent to the non-inverting input terminal (+) of the dewidth remover 18 via the resistors 14 and 16. Applied to the inverting input terminal (-). Also, amplifier 1
An input terminal 20 is formed at the non-inverting input terminal (+) of No. 8, and a signal to be amplified is added thereto.

An output terminal 22 is formed on the output side of the amplifier 18, through which the output is taken out either directly or after being subjected to processing such as amplification using an amplifier (not shown). Further, a power supply terminal 24 is formed on the positive potential line side of the constant current source 4 and the amplifier 18, and a common terminal 26 to be grounded is formed on the common line side, and a driving voltage Vc.c. is added.

In such a bias power supply circuit, the constant current source 4
In order to remove the noise component, a bypass capacitor 12 with a large capacity is required, and the semiconductor integrated circuit device 2 requires a terminal 10 to connect it.

Generally, in a high frequency amplifier circuit, band amplification occupies most of the circuit. The noise of a constant current source is irregularly distributed over a wide band, but when used in a band amplification circuit, it is sufficient that the noise does not fall within the band. Therefore, when a constant current source is installed in the bias power supply circuit, it is sufficient to remove the noise component within the band.

Therefore, an object of the present invention is to provide a bias power supply circuit with low noise. That is, the bias power supply circuit of the present invention has a constant forward direction by supplying a constant current from the constant current source 30. a first diode 28 that generates a voltage drop; a transistor 32 that is biased by the forward voltage drop of this diode and flows a constant current corresponding to the constant current flowing to the constant current source;
a resistor 3 inserted between a connection point between the diode and the constant current source and the base of the transistor;
4, a noise absorbing capacitor 38 installed between the base and collector of the transistor, and a second diode 35 connected in series with the transistor to generate a bias voltage by the current flowing through the transistor. It is something that

Hereinafter, the present invention will be described in detail with reference to embodiments shown in the drawings.

FIG. 2 shows an embodiment of the bias power supply circuit of the present invention, and the same parts as those of the semiconductor integrated circuit device shown in FIG. 1 are given the same reference numerals.

In FIG. 2, in this semiconductor integrated circuit device 2, a first diode 28 is connected between the positive potential line where the power supply terminal 24 is formed and the common line where the common terminal 26 is formed. Current source 3
0 is connected to the cathode of the diode 28,
The base of transistor 32 has a resistor 3 at its input.
Connected via 4.

The transistor 32 is composed of a PNP type transistor, and its emitter is connected to the positive potential line, and a second transistor is connected between its collector and the common line.
A series circuit of a diode 35 and a resistor 36 is connected. A noise absorbing capacitor 38 is connected between the base and collector of the transistor 32.
is connected. This capacitor 38 is composed of a capacitive element formed inside the semiconductor integrated circuit device 2 along with diodes 28 and 35, a constant current source 30, a transistor 32, and resistors 34 and 36.

According to such a configuration, it is possible to remove the noise of the constant current source 30 by the filter effect of the resistor 34 and the capacitor 38, which are internal elements of the semiconductor integrated circuit device 2, except for the externally connected capacitor and its terminal. Therefore, it is possible to reduce the noise of the bias power supply circuit.

Here, the DC gain of transistor 32 is
Av, the value of the resistor 34 is R, and the capacitance of the capacitor 38 is C. Due to the mirror effect of the transistor 32 and the capacitor 38, the noise reduction frequency is determined as follows: =1/R·C·Av. Therefore, when used as a bias power supply circuit for various amplifiers, it is possible to reduce noise at frequencies above the above-mentioned frequency. In particular, the present invention can effectively attenuate noise in a specific frequency band, and is extremely effective in band amplifiers constituting high frequency amplifier circuits, but it can also be used in audio amplifiers.

FIG. 3 shows another embodiment of the present invention, in which a capacitor 40, which is used as an internal element of the semiconductor integrated circuit device 2, is also provided between the base and emitter of the transistor 32.

With this configuration, it is possible to more effectively reduce noise.

As explained above, according to the present invention, it is possible to reduce noise using only the internal elements of a semiconductor integrated circuit device, and omit the conventional external bias capacitor and the terminal for connecting it. The configuration can be simplified.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing a conventional bias power supply circuit, Fig. 2 is a circuit diagram showing an embodiment of the bias power supply circuit of the present invention, and Fig. 3 is a circuit diagram showing another embodiment of the bias power supply circuit of the present invention. It is a diagram. 28...First diode, 30... Constant current source, 32... Transistor, 34... Resistor, 35
...Second diode, 38...Noise absorption capacitor.

Claims (1)

[Claims] 1. A first diode that generates a constant forward voltage drop by being supplied with a constant current by a constant current source, and a bias is set by the forward voltage drop of this diode. a transistor that flows a constant current corresponding to the constant current flowing through the constant current source; a resistor inserted between a connection point between the diode and the constant current source and the base of the transistor; A bias power supply circuit comprising: a noise absorbing capacitor installed between collectors; and a second diode connected in series with the transistor to generate a bias voltage by a current flowing through the transistor. . 2. Claim 1, characterized in that a capacitor formed inside the semiconductor integrated circuit device is installed between the base and collector of the transistor.
Bias power supply circuit described in section.