JPH0497607A - Semiconductor integrated circuit - Google Patents

Abstract

PURPOSE:To vary the capacitance and to warrant a characteristic with respect to a high frequency by providing an internal capacitance connecting to a switching circuit having a constant current source. CONSTITUTION:Whether or not a capacitor C connecting in parallel with a feedback resistor R2 is connected to ground is selected by using a constant current source I and a switching transistor(TR) 2. When the capacitor C connects to ground, a voltage less than 1V, e.g. applied to a switch terminal (SW) to turn on the switching TR 2 and a resistance between the collector and the emitter is decreased. When the capacitor C is opened, the switching TR 2 is opened by opening the SW and the impedance of the collector of the TR 2 with respect to ground is increased. Thus, the capacitance of the capacitor C is made variable and the characteristic of a high frequency amplifier is warranted.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a semiconductor integrated circuit, and more particularly to a grounded emitter type amplifier.

[Conventional technology]

Conventionally, in this type of amplifier, a feedback resistor R2 is inserted between the emitter of the transistor T r 1 used for amplification and the ground, as shown in FIGS. 3 and 4. When widening the frequency characteristic, in order to make the value of the feedback resistor appear smaller in the high frequency band where the gain decreases, it is necessary to install it inside the chip as shown in Figure 3 or externally as shown in Figure 4. A capacitor tc+ or C2 was connected in parallel with the resistor R2.

[Problem to be solved by the invention]

The conventional amplifier circuit described above has the following problems. That is, when building a capacitor internally, since the capacitance value is determined at the stage of building the capacitor, it is necessary to recreate it to correct the value. Furthermore, it is difficult to guarantee manufacturing variations.

On the other hand, when connecting a capacitor externally, the capacitance value is variable because the capacitor is connected externally, but the inductance of the bonding wire between the bonding pad and the package bin is connected in series, so In high frequency bands above IGHz, its influence cannot be ignored.

An object of the present invention is to provide a semiconductor integrated circuit in which operating modes such as gain can be selected and characteristics at high frequencies can be guaranteed.

[Means to solve the problem]

The semiconductor integrated circuit of the present invention includes a transistor whose emitter is connected to a power source via a feedback resistor, a capacitor provided between the emitter of the transistor and the power source, and a control device that controls conduction between the capacitor and the power source. It is characterized by having a means.

〔Example〕

FIG. 1 shows a common emitter amplifier circuit showing a first embodiment of the present invention. Trl is a common emitter transistor, R
1 is a load resistance, and R2 is a feedback resistance. C is feedback resistance R
Whether or not this capacitor C is connected to the ground can be selected by the constant current source I and the switching transistor Tr2.

When connecting the capacitor C to the ground, a weak voltage of IV, for example, is applied to SW. This turns on the switching transistor Tr2, and the collector-emitter resistance decreases.

Furthermore, when the capacitor C is opened, the switching transistor Tr2 becomes inoperable if SW is opened, and the switching transistor Tr2 becomes inoperable.
The impedance between the collector terminal side of No. 2 and the ground becomes high.

With the above configuration, it is possible to vary the capacitance value of the capacitor C according to the voltage of SW.

FIG. 2 is a circuit diagram showing a second embodiment of the present invention. As shown in the figure, Trl is a transistor that operates as a common emitter amplifier, R1 is a load resistance, and R2 is a feedback resistance. The capacitances C1゜C2 and C3 are II and Tri-, respectively.
I2 Tr2-I3. Whether Tr3 is connected in parallel with feedback resistor R2 is controlled.

For example, if the capacitor C1 is set to 1 pF, the capacitor C2 is set to 2 pF, and the capacitor C3 is set to 4 pF, the following capacitor combinations are possible.

When SWI, SW2, SW3 are off... Capacity = Op When only SWI is on... Capacity = 1pF
When only SW2 is on... Capacity = 2 pFS When only SW3 is on... Capacity = 3 pFSWI, when SW2 is on... Capacity = 4 pFSWI, when SW3 is on... Capacity = 5 pFSWI, when SW3 is on ...Capacity=6pFSWI, SW2. SW
3 is on...capacitance = 7pF [As explained in detail, the present invention has an internal capacitance connected to a switching circuit containing a constant current source, so even though there is a capacitance inside the chip, , connection or not can be controlled externally by switching, and the capacitance value can be varied.

Moreover, since no feedback path is drawn out to the outside, the influence of the inductance of the bonding wire can be ignored, which not only guarantees the characteristics especially in high-frequency amplifiers, but also allows the configuration of amplifiers with selectable operating modes such as gain. becomes.

It is a circuit diagram.

R1...Load resistance, R2...Feedback resistance, Trl...
・Amplification transistor, Tr2... Switching transistor, ■... Constant current source, C... Capacity, C1...
...Capacitance, C2...External capacitance, Ll...Bonding wire inductance, SW...Switch terminal,
Vcc...power supply, IN, OUT...signal input/output.

Claims (1)

[Claims] A transistor having an emitter connected to a power source via a feedback resistor, a capacitor provided between the emitter of the transistor and the power source, and a control means for controlling conduction of the capacitor with the power source. semiconductor integrated circuits.