Miscellaneous active electrical nonlinear devices – circuits – and – Specific signal discriminating without subsequent control – By amplitude
Reexamination Certificate
2000-11-01
2001-11-06
Tran, Toan (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Specific signal discriminating without subsequent control
By amplitude
C330S261000
Reexamination Certificate
active
06313667
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the field of amplifiers, and in particular, to a turn around stage with Class AB behavior, low power consumption, low noise and improved offset performance.
BACKGROUND OF THE INVENTION
An integrated amplifier circuit such as an opamp is usually constructed from a small chip of semiconductor material upon which an array of active/passive components have been constructed and connected together to form a functioning circuit. An integrated amplifier circuit is generally encapsulated in a plastic housing (chip) with signal, power supply, and control pins accessible for connection to external electronic circuitry. Typically, input signals transmitted to the integrated amplifier circuit via selected input pins are processed by active and passive components in different stages, e.g., input and turn-around, and the processed signals are then applied to selected output pins using an output stage.
The enormous growth of high-speed communication and high data rate image processing applications, requiring high-speed, low power and small size, has created a demand for miniaturized high-speed amplifiers that can operate at low voltages. To maximize the dynamic range at low supply voltages for this use, it is desirable that the output voltage range for this type of amplifier should be as large as possible. Preferably, the output voltage range of the amplifier would extend from one rail to the other rail of the power supply.
Class-AB circuitry is used in amplifiers that employ both bipolar and MOS components. A Class AB circuit can deliver to and pull from a load a current that is larger than the DC quiescent current flowing into the circuit. Class AB circuitry is preferred in output stage of a low-power high speed amplifier because it improves power efficiency by maximizing the output drive current with a relatively low quiescent current. For example, the drive current for a Class AB circuit might be 100 milliamps and the quiescent current could be 1 milliamps. Also, Class AB circuitry exhibits good linearity over the entire output voltage range.
A turn around or level-shift stage is an often neglected, but crucial part of an amplifier. Its main purpose is providing a level shift function, such that the input common mode voltage range of the amplifier is independent of the output voltage. Because the turn around stage often directly follows an input stage, the turn around stage is usually an important contributor to input non-ideal parameters such as offset and noise. In many cases, the turn around stage can be the dominant factor for these parameters, and sometimes even more so than the input stage itself.
SUMMARY OF THE INVENTION
In accordance with the invention, an apparatus for a circuit with an input common mode voltage range that is independent of the output voltage range is disclosed. An input stage is adapted for receiving an input signal. A first current source is coupled to an emitter of a first transistor and an emitter of a second transistor. A current provided by the first current source is evenly split between the emitters of the first and second transistors when a polarity of the input signal is equal. Alternatively, when one of the first and second transistors is activated by an unequal polarity of the input signal and the other of the first and second transistors is deactivated, the current provided by the first current source flows mainly through one of the first and second transistors that is activated. A turn around stage outputs an output signal when the polarity of the input signal is unequal. A second current source is coupled to a collector of a third transistor and a third current source is coupled to a collector of a fourth transistor. The flow of the current through the one of the first and second switches that is activated causes one of the third and fourth switches to be deactivated and another one of the third and fourth switches to be activated. The one of the third and fourth transistors that is activated conducts an output current from one of the second and third current sources that is substantially larger than another current that flows through the other one of the third and fourth switches that is deactivated. A bias circuit separately provides a floating bias for the operation of the third and fourth transistors. A base and a collector of a fifth transistor is coupled to a base of the third transistor. A fourth current source and an emitter of the fifth transistor is cross coupled to an emitter of the fourth transistor. A base and a collector of a sixth transistor is coupled to a base of the fourth transistor. The fourth current source and an emitter of the sixth transistor is cross coupled to an emitter of the third transistor.
In accordance with another aspect of the invention, a first resistor is coupled between the fourth current source and the base and the collector of the fifth transistor. Also, a second resistor is coupled between the fourth current source and the base and the collector of the sixth transistor. A value of the first resistor and another value of the second transistor are matched so that a total current provided by the fourth current source is split evenly between a current that flows through the fifth transistor and another current that flows through the sixth transistor. It is further envisioned that the difference between the value of the first resistor and the other value of the second transistor is less than a tenth of a percent. The cross coupling of the emitters of the fifth and sixth transistors and the arrangement of the first and second resistors reduces noise, offset and power consumption of the circuit.
In accordance with yet another aspect of the invention, the first and second transistors are PNP bipolar transistors, the third and fourth transistors are NPN bipolar transistors and the fifth and sixth transistors are NPN bipolar transistors. Also, each current flowing through the fifth and sixth transistors are equal and constant both when the polarity of the input signal is equal and when the polarity of the input signal is unequal.
In accordance with still another aspect of the invention, a third resistor has one end coupled to a negative rail of a voltage supply and another end coupled to the collector of the first transistor, the emitter of the third transistor and the emitter of the fifth transistor. Also, a fourth resistor has one end coupled to the negative rail of the voltage supply and another end coupled to the collector of the first transistor, the emitter of the fourth transistor and the emitter of the sixth transistor, so that a current flowing through the third resistor matches another current flowing through the fourth resistor. Additionally, a fifth resistor has one end coupled to the first current source and another end coupled to the emitter of the first transistor. A sixth resistor has one end coupled the first current source and another end coupled to the emitter of the second transistor.
In accordance with another aspect of the invention, the output current that flows through the one of the third and fourth transistors that is activated is substantially equal to the current that flows through the one of the first and second transistors that is activated by the unequal polarity of the input signal. The first, second, third and fourth current sources are coupled to a positive rail of a voltage supply. Also, the first, second, third and fourth current sources include at least one resistor and at least one transistor. Additionally, the invention provides Class AB behavior.
In accordance with yet another aspect of the invention, the input signal is received across a base of the first transistor and a base of the second transistor. Also, the output signal is provided across the collectors of the third and fourth transistors.
In accordance with further aspects of the invention, a complementary input stage is adapted to receive a differential input signal with a common mode voltage that can be at, or between, the rails of a voltage supply. Also, a pair
Branch John W.
Merchant & Gould P.C.
National Semiconductor Corporation
Tran Toan
LandOfFree
Apparatus and method for a turn around stage having reduced... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Apparatus and method for a turn around stage having reduced..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Apparatus and method for a turn around stage having reduced... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2605606