1. Technical Field
The present invention relates to an amplifying circuit of a semiconductor integrated circuit, and more particularly, to an amplifying circuit of a semiconductor integrated circuit that is capable of amplifying input data having a small level difference between logic levels.
2. Related Art
Referring to FIG. 1, a conventional amplifying circuit of a semiconductor integrated circuit includes a differential amplifying unit 10 and a cross coupled amplifying unit 20.
The differential amplifying unit 10 performs primary amplification on input data IN and INb whose level difference is very small in accordance with a first control signal STB1, and outputs a first up-signal OUT1 and a first down-signal OUT1b. 
The cross coupled amplifying unit 20 performs secondary amplification on the level difference between the first up-signal OUT1 and the first down-signal OUT1b in accordance with a second control signal STB2, and outputs a second up-signal OUT2 and a second down-signal OUT2b of logic levels.
The first control signal STB1 activates the differential amplifying unit 10, and the second control signal STB2 activates the cross coupled amplifying unit 20.
In the amplifying circuit of the semiconductor integrated circuit according to the related art, when the level difference between the input data IN and INb is very small, the differential amplifying unit 10 performs primary amplification on the level difference between the input data IN and INb. Then, the cross coupled amplifying unit 20 amplifies the level difference between the first up-signal OUT1 and the first down-signal OUT1b, which are output by the differential amplifying unit 10, to a logic level.
The differential amplifying unit 10 may be composed of a plurality of differential amplifiers. For example, as shown in FIG. 1, when the differential amplifying unit 10 is composed of two differential amplifiers, one differential amplifier amplifies the level difference between the input data IN and INb and outputs the first up-signal OUT1. The other differential amplifier amplifies the level difference between the input data IN and INb and outputs the first down-signal OUT1b that has a phase opposite to a phase of the first up-signal OUT1.
The cross coupled amplifying unit 20 receives the first up-signal OUT1 and the first down-signal OUT1b, and amplifies the level difference between the first up-signal OUT1 and the first down-signal OUT1b by an internal feedback operation of the cross coupled amplifying unit 20. Accordingly, the cross coupled amplifying unit 20 outputs the second up-signal OUT2 and the second down-signal OUT2b of the logic levels by the internal feedback operation.
That is, the differential amplifying unit 10 detects the small level difference between the input data IN and INb and amplifies the input data IN and INb so as to be detected by the cross coupled amplifying unit 20. The cross coupled amplifying unit 20 amplifies potential levels of the first up-signal OUT1 and the first down-signal OUT1b, which are output by the differential amplifying unit 10, to the logic levels.
The differential amplifying unit 10 amplifies the level difference between the input data IN and INb by a self gain. Therefore, the differential amplifying unit 10 can perform an amplifying operation stably even if the differential amplifying unit 10 is affected by an offset or noise. However, when signal levels of the input data IN and INb are low, the differential amplifying unit 10 does not amplify potential levels of the first up-signal OUT1 and the first down-signal OUT1b to the logic levels. Meanwhile, the cross coupled amplifying unit 20 can amplify the potential levels of the first up-signal OUT1 and the first down-signal OUT1b to the logic levels by the feedback operation. However, erroneous feedback may occur due to the offset or noise.
The amplifying circuit of the semiconductor integrated circuit according to the related art uses advantages of the differential amplifier and the cross coupled amplifier.
That is, the differential amplifying unit 10 amplifies input data stably by a self gain, and the cross coupled amplifying unit 20 amplifies the potential levels of the first up-signal OUT1 and the first down-signal OUT1b that are output by the differential amplifying unit 10 to the logic levels, and outputs the second up-signal OUT2 and the second down-signal OUT2b. However, since two amplifying steps are needed to amplify one signal, a circuit area is large. In particular, when a large amount of input/output sense amplifiers are used in a semiconductor memory device, the input/output sense amplifiers occupy a relatively large area in the semiconductor integrated circuit.