GB2054307A - Integrated circuit capacitors - Google Patents

Abstract

A bipolar transistor structure, typically a lateral pnp transistor, is used as an integrated circuit capacitor, the transistor being operated at frequencies above its transition frequency. In a typical balanced RF amplifier circuit such equivalent capacitors (T1, T2) are used as oscillation- suppressing and amplifying elements in the feedback network. <IMAGE>

Description

SPECIFICATION Integrated circuit capacitors This invention relates to bipolar integrated circuits, and in particular to capacitance structures for such circuits.

Bipolar integrated circuits, i.e., both their semiconductor structure and their circuit technology, are described, for example, in the journal "Scientia electrica", 1963, pages 67 to 91. While active components, i.e., transistor structures and diode structures, and resistors are relatively easy to integrate, the integration of capacitors poses certain problems.

According to pages 81 to 83 of the above reference, these problems are essentially due to the fact that, for economic reasons, i.e., for lack of space, capacitors of the order of only about 1 nF can be realized. At the present time, therefore, capacitors of higher value are not integrated but connected via external terminals of the integrated circuit. This, however, requires at least one external terminal (if one terminal of the capacitor is grounded or connected to the supply voltage) or even two external terminals (if the capacitor is inserted between two circuit points not normally connected to the outside).

In special applications, attempts have been made to obviate this difficulty by developing specific circuits which require lower capacitances than the known circuits, so that integrated capacitors can be realized.

According to one aspect of the invention there is provided an integrated circuit comprising a capacitor in the form of a bipolar transistor structure which when operated at frequencies above the transition frequency of the transistor structure will act as the capacitor.

According to another aspect of the invention there is provided a balanced amplifier circuit, including a plurality of differential amplifier stages each provided with one or more pairs of transistors of the same conductivity type, and wherein negative feedback is provided by a pair of bipolar transistors of the complementary type to the amplifier transistors, the feedback transistors being operated at a frequency above their transistor frequency whereby the feedback transistors function as capacitors.

The invention will now be explained in more detail with reference to the accompanying drawing, whose single figure illustrates a balanced RF amplifier constructed on the differential-amplifier principle. Its cut-off frequency is of the order of one gigahertz, in the present case about 1.5 GHz. A negativefeedback arm from the output to the input of the amplifier is used to stabilize the DC operating point in the known manner. The negative-feedback arm contains two transistor structures operated in the active region and having a transition frequency lower than the amplifier's cut-off frequency; preferably, the transition frequency is lower than the lowest operating frequency of the amplifier.

1. An integrated circuit comprising a capacitor in the form of a bipolar transistor structure which when operated at frequencies above the transition frequency of the transistor structure will act as the capacitor.

2. A circuit as claimed in claim 1 wherein the transistor structure comprises a lateral pnp-transistor.

3. An integrated circuit having a capacitor substantially as described herein with reference to the accompanying drawing.

4. A monolithic integrated RF amplifier using a bipolar transistor structure as claimed in claim 1 or 2 both as an oscillation-suppressing capacitor and as an active component in the negative feedback arm.

5. A semiconductor amplifier circuit, including a plurality of bipolar transistors of the one conductivity type, wherein negative feedback is provided a capacitor provided by a bipolar transistor structure complementary in type to the amplifier transistor operated at a frequency above its transistor frequency.

6. A balanced amplifier circuit, including a plurality of differential amplifier stages each provide with one or more pairs of transistors of the same conductivity type, and wherein negative feedback is provided by a pair of bipolar transistors of the complementary type to the amplifier transistors, the feedback transistors being operated at a frequency above their transition frequency whereby the feedback transistors function as capacitors.

7. A balanced amplifier substantially as described herein with reference to the accompanying drawing.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (7)

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Integrated circuit capacitors This invention relates to bipolar integrated circuits, and in particular to capacitance structures for such circuits. Bipolar integrated circuits, i.e., both their semiconductor structure and their circuit technology, are described, for example, in the journal "Scientia electrica", 1963, pages 67 to 91. While active components, i.e., transistor structures and diode structures, and resistors are relatively easy to integrate, the integration of capacitors poses certain problems. According to pages 81 to 83 of the above reference, these problems are essentially due to the fact that, for economic reasons, i.e., for lack of space, capacitors of the order of only about 1 nF can be realized. At the present time, therefore, capacitors of higher value are not integrated but connected via external terminals of the integrated circuit. This, however, requires at least one external terminal (if one terminal of the capacitor is grounded or connected to the supply voltage) or even two external terminals (if the capacitor is inserted between two circuit points not normally connected to the outside). In special applications, attempts have been made to obviate this difficulty by developing specific circuits which require lower capacitances than the known circuits, so that integrated capacitors can be realized. According to one aspect of the invention there is provided an integrated circuit comprising a capacitor in the form of a bipolar transistor structure which when operated at frequencies above the transition frequency of the transistor structure will act as the capacitor. According to another aspect of the invention there is provided a balanced amplifier circuit, including a plurality of differential amplifier stages each provided with one or more pairs of transistors of the same conductivity type, and wherein negative feedback is provided by a pair of bipolar transistors of the complementary type to the amplifier transistors, the feedback transistors being operated at a frequency above their transistor frequency whereby the feedback transistors function as capacitors. The invention will now be explained in more detail with reference to the accompanying drawing, whose single figure illustrates a balanced RF amplifier constructed on the differential-amplifier principle. Its cut-off frequency is of the order of one gigahertz, in the present case about 1.5 GHz. A negativefeedback arm from the output to the input of the amplifier is used to stabilize the DC operating point in the known manner. The negative-feedback arm contains two transistor structures operated in the active region and having a transition frequency lower than the amplifier's cut-off frequency; preferably, the transition frequency is lower than the lowest operating frequency of the amplifier. CLAIMS

1. An integrated circuit comprising a capacitor in the form of a bipolar transistor structure which when operated at frequencies above the transition frequency of the transistor structure will act as the capacitor.

2. A circuit as claimed in claim 1 wherein the transistor structure comprises a lateral pnp-transistor.

3. An integrated circuit having a capacitor substantially as described herein with reference to the accompanying drawing.

4. A monolithic integrated RF amplifier using a bipolar transistor structure as claimed in claim 1 or 2 both as an oscillation-suppressing capacitor and as an active component in the negative feedback arm.

5. A semiconductor amplifier circuit, including a plurality of bipolar transistors of the one conductivity type, wherein negative feedback is provided a capacitor provided by a bipolar transistor structure complementary in type to the amplifier transistor operated at a frequency above its transistor frequency.

6. A balanced amplifier circuit, including a plurality of differential amplifier stages each provide with one or more pairs of transistors of the same conductivity type, and wherein negative feedback is provided by a pair of bipolar transistors of the complementary type to the amplifier transistors, the feedback transistors being operated at a frequency above their transition frequency whereby the feedback transistors function as capacitors.

7. A balanced amplifier substantially as described herein with reference to the accompanying drawing.