Amplifiers – With semiconductor amplifying device – Including differential amplifier
Reexamination Certificate
1999-10-28
2001-07-10
Pascal, Robert (Department: 2817)
Amplifiers
With semiconductor amplifying device
Including differential amplifier
C330S252000, C330S253000, C330S260000
Reexamination Certificate
active
06259322
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
This invention relates generally to the field of electronic amplifier circuits, and more particularly to a low power, low noise differential gain amplifier circuit.
BACKGROUND OF THE INVENTION
The recent miniaturization trend in electronic circuit designs is driven by consumer demand for smaller and light-weight electronic devices such as cellular phones and portable computers, for example. Often, the heaviest component in an electronic device is the battery. Devices having smaller batteries require low power electronic circuits to prevent the battery from discharging too rapidly. Logic integrated circuits (ICs) have migrated to lower working voltages in the search for lower power consumption and higher operating frequencies.
An amplifier is a linear electronic circuit that may be used amplify an input signal and provide an output signal that is a magnified replica of the input signal. Amplifiers are used in a variety of electronic circuit design applications. As appliances and circuit designs continue to decrease in size and increase in speed, the need for low power, low noise, current efficient amplifier circuitry increases.
SUMMARY OF THE INVENTION
The present invention achieves technical advantages as a low noise, low current high bandwidth differential amplifier circuit using matched current mirrors and having single stage op amps. The low power circuit is useful in a variety of applications, particularly in small portable electronic devices such as cellular phones and laptop computers.
In one embodiment, disclosed is a low noise, low current, high bandwidth differential amplifier circuit including a first amplifier driving a first transistor and having a first current source coupled to an input of the first amplifier. A first resistor is coupled between the first current source and the first transistor, and a second resistor is coupled to the first transistor. A second amplifier drives a second transistor, and a second current source is coupled to an input of the second amplifier. A third resistor is coupled between the second current source and the second transistor. A fourth resistor is coupled to the third resistor. The first and third resistors are driven by the first and second current sources, respectively, rather than by the first and second amplifiers, respectively.
In another embodiment, disclosed is a low noise, low current, high bandwidth differential amplifier circuit, having a first amplifier driving the gate of a first transistor. A first current mirror circuit is coupled to the drain of the first transistor, and a first current source is coupled to an input of the first amplifier. A first resistor is coupled between the first current source and the source of the first transistor. A second resistor is coupled to the first transistor source. A second amplifier drives the gate of a second transistor. A second current mirror circuit is coupled to the drain of the second transistor, and a second current source is coupled to an input of the second amplifier. A third resistor is coupled between the second current source and the second transistor source. A fourth resistor is coupled to the third resistor. The second and fourth resistors are coupled to each other at a node. The first and third resistors are driven by the first and second current sources, respectively, rather than by the first and second amplifiers, respectively.
Also disclosed is a differential amplifier circuit having a first branch coupled to a second branch. The first branch includes a first amplifier having a first and second input terminal and driving a first transistor, where the first input terminal is non-inverting and adapted to receive a positive input voltage signal. A first current source is coupled to the first amplifier inverting second input terminal, with a first resistor being coupled between the first current source and the first transistor. The first branch also includes a second resistor coupled to the first resistor, whereby a positive output voltage is generated at the second resistor. The second branch includes a second amplifier having a first and second input terminal and driving a second transistor. The second amplifier first input terminal is non-inverting and is adapted to receive a negative input voltage signal. The second branch has a second current source coupled to the second amplifier inverting second input terminal. A third resistor is coupled between the second current source and the second transistor. A fourth resistor is coupled at one end to the third resistor, with a negative output voltage being at the other end of the fourth resistor. The second and fourth resistors are coupled to each other at a node. The first and third resistors are driven by the first and second current sources, respectively, rather than by the first and second amplifiers, respectively.
In another embodiment, disclosed is a method of amplifying a differential electrical input signal in a differential amplifier circuit having a first and second branch. Each branch includes an amplifier driving a respective transistor, each amplifier having a feedback resistor and an output resistor. The branches are coupled together at the output resistors. The method includes the steps of driving the feedback resistors with a respective first current source, and generating an output signal at the output resistors.
The present invention is advantageous in providing a low noise, low current, high bandwidth differential amplifier circuit. Because the first and second amplifiers do not drive the first and third resistors, they can be simpler, single stage amplifiers. This reduces power consumption and saves semiconductor real estate. The present invention provides a low power way of achieving a closed loop voltage gain with low noise. The need for an output stage has been removed so that simple single-stage op amps may be used for the amplifiers, which translates to wide bandwidth. The amplifiers have a very high input impedance and small resistors may be used. Furthermore, the circuit has great flicker and thermal noise performance. The gain and bandwidth are independent of one another, rather than being a function of one another as in prior art circuits. The Gain-Bandwidth Product (GBP) relationship in prior art circuits does not apply for the present invention. Also, total harmonic distortion (THD) and power supply rejection ratio (PSRR) performance is maximized by the present invention. Gain is determined by the resistor ratio, through size variations of the transistors that comprise the current mirror circuits, or a combination thereof.
REFERENCES:
patent: 4999585 (1991-03-01), Burt et al.
patent: 5128630 (1992-07-01), Mijuskovic
patent: 5157347 (1992-10-01), Geerdink et al.
patent: 5825247 (1998-10-01), Herrlinger
Brady III Wade James
Holmbo Dwight N.
Nguyen Patricia T.
Pascal Robert
Telecky , Jr. Frederick J.
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