Amplifiers – With semiconductor amplifying device – Including gain control means
Reexamination Certificate
2000-12-13
2001-08-21
Pascal, Robert (Department: 2817)
Amplifiers
With semiconductor amplifying device
Including gain control means
C330S278000, C330S254000
Reexamination Certificate
active
06278325
ABSTRACT:
1. FIELD OF THE INVENTION
The present invention relates to a programmable gain amplifier, and especially to a programmable gain amplifier with a large extent for the variation of gains, which is made by a manufacturing process of complementary metal oxide semiconductor (CMOS) or a bipolar junction transistor(BJT).
2. BACKGROUND OF THE INVENTION
Programmable gain amplifiers are very important in wireless communication system (such as GSM) requiring highly dynamic range. Therefore, a programmable gain amplifier with a larger gain controllable range and highly controllable linearity is beneficial to the whole effect of the system and complexity of the system. The gain control of a programmable gain amplifier can be achieved by changing the direct bias current (change gm of a transistor) and load resistance of an amplifier, wherein the maximum gain change is to control the bias current.
FIG. 1
shows a programmable gain amplifier with a varied gain range in the prior art design (U.S. Pat. No. 4,394,777), wherein the programmable gain amplifier includes a reference current generating circuit, a plurality of resistor elements, an auxiliary reference voltage generator, a plurality of switches which are connected to the resistor elements and a voltage to current converter. In the current gain control method, OP feedback circuit serves to control the depth of a MOS switch for adjusting the direct bias current of an amplifier or using fixed voltage to switch load resistor for change the value of current. While the abovesaid method has the following disadvantages: 1. The OP feedback circuit has a problem of stability. 2. It is difficult to control the depth of MOS switch. 3. The fixing voltage is used in the MOS manufacturing process, the variation of V
T
causes that the performance of the circuit can not be controlled. 3. The layout of the resistors occupys a large area and the error in manufacturing process is large. 4. The structure of the circuit is complex. 5. Extra power consumption is required.
SUMMARY OF THE INVENTION
In order to increase the varied range of a gain and the precision of each gain level, and to be suitable for a low cost CMOS manufacturing process, the present invention discloses a new circuit structure for the current technology defect, and meanwhile, the difficult in design is reduced.
To achieve the aforesaid object, the present invention provides a programmable gain amplifier with a large extent for the variation of gains made by a manufacturing process of compensated metal oxide semiconductor or a bipolar junction transistor is disclosed. The structure is divided into two stages, a first stage and a second stage. The first stage is formed by connecting a plurality of transistors in parallel, and the second stage is formed by a further plurality of transistors in parallel. The first stage and the second stage are connected in series. The current output end of transistors in the first stage each are connected to respective switches, respectively. Another, the current input end of transistors in the second stage each are connected to respective switches, respectively. Each of the switches is connected to a decoder. Therefore, through the control of the decoder, the on and off conditions of the switches can be determined so as to derive the required bias current.
One of the programmable gain amplifier with a large extent for the variation of gains is made by a manufacturing process of compensated metal oxide semiconductor. The amount of current is determined wholly from the ratio of the transistor, therefore, the effect of error to the manufacturing process and the shift of temperature is very small. In a compensated metal oxide semiconductor, the gain in a amplifying stage is positively proportional to the transconduce (gm), while the value of gm is positively proportional to the square root value of the bias current (in bipolar, the gm is positively proportional to the bias current). Therefore, in the CMOS circuit, as the varied range of a programmable gain amplifier is enlarged, the varied range of the bias current in the gain stage is also very large, while the circuit structure of the present invention is suitable for this operation, otherwise, the advantages of this design core as following. The gates of CMOSs are not biased directly, therefore, the voltage change in the gate of the CMOS from errors will not effect the work of the circuit. The extra current consumed in the bias current can be avoided so as to achieve the object of power-saving. No resistance is used in the biasing and current control. Comparing with the way of controlling current by serially connecting resistors, the present invention uses smaller layout space and the effect of the error in the manufacturing process is reduced greatly. The required bias current is independently controlled by switches. For an amplifier necessary to precisely controlling the variation of gain, the difficult in design can be reduced.
REFERENCES:
patent: 5999052 (2001-01-01), Tang
patent: 6049252 (2000-04-01), Iwata
patent: 6157259 (2000-12-01), Dasgupta
patent: 6175278 (2001-01-01), Hasegawa
Choe Henry
Industrial Technology Research Institute
Pascal Robert
LandOfFree
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