US 2006/0223474 A1 · Semiconductor integrated circuit

Abstract

In a communication semiconductor integrated circuit, a capacitance included in a filter on the output side of a mixer circuit is reduced without requiring the cutoff frequency of the filter to be changed. A Gilbert cell circuit is used as a mixer circuit which combines, for downconversion, a reception signal and a local oscillator signal. A low-pass filter for removing unwanted waves from output is composed of load resistors of upper stage differential transistors and a capacitive element provided between differential output terminals. The resistances of the load resistors are increased, and a current circuit for applying a current to emitters or collectors of the upper stage differential transistors is provided, so that a current to make up for a decrease in current amount attributable to the increase in load resistance can be applied from the current circuit to lower stage differential transistors.

Claims10

Dependent claims

A semiconductor integrated circuit, comprising:

a first transistor through which a direct current and an alternate current corresponding to an input signal of a first frequency are passed;
a second transistor, to an emitter or source of which an output current from a collector or drain of the first transistor is inputted, to a control terminal of which a signal of a second frequency is applied, and from a collector or drain of which a signal generated by combining the input signal of the first frequency and the signal of the second frequency is outputted;
and
a low-pass filter including a load resistor and a capacitive element and being connected to the collector or drain of the second transistor;
wherein a current injection circuit for applying a part of the direct current passing through the first transistor without making the part of the direct current pass through the load resistor is provided, and
wherein the load resistor and the capacitive element are formed on a semiconductor substrate where the first transistor and the second transistor are also formed.

3 more elements

A semiconductor integrated circuit, comprising:

a first pair of transistors through which a direct current and an alternate current corresponding to a differential input signal of a first frequency are passed;
second and third pairs of transistors, to common emitters or common sources of which output currents from collectors or drains of the first pair of transistors are inputted respectively, to control terminals of which a differential signal of a second frequency is applied, and from collectors or drains of which a differential signal generated by combining the differential input signal of the first frequency and the differential signal of the second frequency is outputted;
and
a low-pass filter which includes a first load resistor connected to one of common collectors or one of common drains of the second and third pairs of transistors, a second load resistor connected to the other of the common collectors or the other of the common drains of the second and third pairs of transistors, and a capacitive element connected between the one of the common collectors or the one of the common drains of the second and third pairs of transistors and the other of the common collectors or the other of the common drains of the second and third pairs of transistors;
wherein a current injection circuit for applying a part of the direct current passing through the first pair of transistors without making the part of the direct current pass through the first and second load resistors is provided, and
wherein the first and second load resistors and the capacitive element are formed on a semiconductor substrate where the first, second and third pairs of transistors are also formed.

3 more elements

Dependencies are inferred from the claim text.

Semiconductor integrated circuit

Life of this patent

Semiconductor integrated circuit

Life of this patent

Abstract

Claims10