Selectable gain amplifier

A selectable gain amplifier in a standard integrated circuit package configuration comprises an amplifier having an analog input, an output and a control input for selecting one of two or three possible gains for the operational amplifier. A plurality of selectable gain amplifiers may be in a standard integrated circuit package configuration, each having a gain control input for selection of the two or three possible gains. The gain control input replaces an inverting input of a standard operational amplifier and the analog input is the a non-inverting input of the operational amplifier or visa-versa. All other characteristics of the selectable gain amplifier may be the same or similar to a standard operational amplifier. The selectable gain amplifier(s) may be packaged in industry standard integrated circuit packages having standard pin-outs so that they may be compatible as replacement analog amplifiers for existing technology operational amplifier integrated circuit packages.

FIELD OF THE INVENTION

The present invention relates generally to semiconductor integrated circuits, and more particularly to gain selection in semiconductor integrated circuit operational amplifiers.

BACKGROUND OF THE INVENTION TECHNOLOGY

Modern electronic equipment uses analog semiconductor integrated circuits for operation thereof. The analog semiconductor integrated circuits receive analog inputs from various sources, e.g., analog voltage signals such as from sensors, a current-to-voltage converter (resistor), etc., and/or may output analog voltage levels, e.g., analog meter, audio and video applications, servo control, etc. Typically, analog signals must be amplified and/or isolated from an input or an output, and may require impedance transformations from a very high impedance source to driving a low impedance load. Analog operational amplifiers are well suited to perform the aforementioned functions since they are low cost and easily configured for a desired gain with just a few basic parts. Operational amplifiers have become so popular that they are available in many of the standard integrated circuit packages with a substantially uniform pin-out for each of these integrated circuit packages.

Generally, the voltage gain of an operation amplifier may be defined by one or two resistors. So an electronic system using analog input and/or output signals and requiring analog amplification, isolation and/or impedance matching may comprise a plurality of operational amplifiers and gain setting resistors associated therewith. Operational amplifiers in integrated circuit packages are space efficient when used in high density printed circuit boards, however, the gain setting resistors, even the surface mount style, are generally discrete components and take up a lot more circuit board space for what they contribute to the overall electronic system.

Programmable gain operational amplifiers are available that do not require any external gain setting resistors, however, these programmable gain operational amplifiers are generally more complex and are designed for more sophisticated and complex applications than a standard operational amplifier. In addition, the programmable gain operational amplifiers may be packaged and have different pin-outs, e.g., additional pins for gain control, then standard operational amplifiers, and thereby cannot be used as direct replacements in existing electronic circuit board designs. The programmable gain operational amplifiers are generally more expensive than standard operational amplifiers because of their more complex circuitry and lower manufacturing volume compared to the costs and volumes of standard operational amplifiers.

Therefore, what is needed is an analog amplifier in an integrated circuit package that does not require gain setting resistors, has gain selection options and is compatible with existing printed circuit board layouts and integrated circuit package pin-outs.

SUMMARY OF THE INVENTION

The invention overcomes the above-identified problems as well as other shortcomings and deficiencies of existing technologies by providing an analog amplifier in an integrated circuit package that does not require gain setting resistors, has gain selection options and is compatible with existing printed circuit board layouts and integrated circuit package pin-outs.

According to embodiments of the invention, a selectable gain amplifier in a standard integrated circuit package configuration comprises an analog amplifier having an analog input, an output and a gain control input for selecting one of two or three possible gains for the operational amplifier. A plurality of selectable gain amplifiers in a standard integrated circuit package configuration, each having a gain control input for selection of the two or three possible gains, is also contemplated herein. The gain control input may replace an inverting input of a standard operational amplifier and the analog input may be a non-inverting input of the operational amplifier. All other characteristics of the selectable gain amplifier may be the same or similar to a standard operational amplifier. It is also contemplated herein that the inverting input may be used as the analog input and what would have been the non-inverting input used as a gain control input. Up to three gain blocks may be selected through the gain control input by applying a positive supply voltage (e.g., logic level high), a common or ground supply voltage (e.g., logic level low) and no connection or a high impedance connection (e.g., floating input). One of these three input levels may be selected by a hardwired jumper, printed circuit board land, absence of either, or by a tri-state output from a digital logic circuit, e.g., each of the three gains may be selected dynamically through software and/or firmware from an output of a digital logic device or circuit, e.g., a digital processor, microcontroller, microprocessor, application specific integrated circuit (ASIC), programmable logic array (PLA), digital signal processor (DSP), and the like. It is also contemplated and within the scope of the invention that one of two gains may be selected by using a jumper from the gain control input to a common or power supply voltage (e.g., logic level low or logic level high, respectively), or a jumper may be used from either a common or a power supply voltage for a first gain, and no jumper, e.g., gain control input unconnected for a second gain. The analog amplifier may be an operational amplifier, an operational transconductance amplifier (OTA), and the like.

A technical advantage of the invention is a replacement device for existing analog circuit designs. Another technical advantage is gain selection by a digital device. Still another advantage is more compact designs of electronic equipment requiring analog circuits. Another advantage is selection of one of three gains with a single control input. Still another advantage is selection of two gains with a single control input.

Features and advantages of the invention will be apparent from the following description of the embodiments, given for the purpose of disclosure and taken in conjunction with the accompanying drawing.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

A selectable gain amplifier in a standard integrated circuit package configuration comprises an operational amplifier having an analog input, an output and a gain control input for selecting one of two or three possible gains for the operational amplifier. A plurality of selectable gain amplifiers in a standard integrated circuit package configuration, each having a gain control input for selection of the two or three possible gains, is also contemplated herein. The gain control input may replace an inverting input of a standard operational amplifier and the analog input may be a non-inverting input of the operational amplifier. All other characteristics of the selectable gain amplifier may be the same or similar to a standard operational amplifier. It is also contemplated herein that the inverting input may be used as the analog input and what would have been the non-inverting input used as a control input.

One of three gains may be selected through the control input by applying a positive supply voltage (e.g., logic level high), a common or ground supply voltage (e.g., logic level low) and no connection or a high impedance connection (e.g., floating input). One of these three input levels may be selected by a hardwired jumper or printed circuit board land, or by a tri-state output from a digital logic circuit, e.g., each of the three gains may be selected dynamically through software and/or firmware from an output of a digital logic device or circuit, e.g., a digital processor, microcontroller, microprocessor, application specific integrated circuit (ASIC), programmable logic array (PLA), digital signal processor (DSP), and the like.

One of two gains may be selected through the gain control input by applying a positive supply voltage (e.g., logic level high) or a common or ground supply voltage (e.g., logic level low) thereto. The one of two gains may be selected through the gain control input by applying either a positive supply voltage (e.g., logic level high) or a common or ground supply voltage (e.g., logic level low), or no connection to the gain control input. Thus, a voltage or current source or sink at the gain control input selects a first gain and no connection, e.g., substantially an open circuit may select a second gain. The one of two gains may be selected by logic level outputs from a digital logic circuit, e.g., a digital processor, microcontroller, microprocessor, application specific integrated circuit (ASIC), programmable logic array (PLA), digital signal processor (DSP), and the like.

Referring now to the drawings, the details of exemplary embodiments of the invention are schematically illustrated. Like elements in the drawing will be represented by like numbers, and similar elements will be represented by like numbers with a different lower case letter suffix.

Referring toFIG. 1, depicted is a schematic diagram of a prior art non-inverting operational amplifier having a voltage gain of one. An operational amplifier102is connected in an non-inverting configuration having an amplification of one. A resistor R0is connected between the output104and the inverting input108. The value of resistor R0is arbitrary and may be chosen to equal the source resistance connected to the non-inverting input106, or the resistor R0may be substantially a conductor between the output104and the input108.

Referring toFIG. 2, depicted is a schematic diagram of a prior art non-inverting operational amplifier having a voltage gain of greater than one. An operational amplifier102is connected in an non-inverting configuration having amplification, A, determined by resistor R1and resistor R2, i.e., A=1+(R1/R2). The resistor R1is connected between the output104and the inverting input108. Resistor R2is connected between the inverting input108and a circuit common110. Two discrete resistors are required in addition to the operational amplifier.

Referring toFIG. 3, depicted is a schematic diagram of a specific embodiment of a selectable gain amplifier. A selectable gain amplifier302comprises an output304, a non-inverting input306and a gain control input308. The gain control input308may be used to select one of three gains at which the amplifier302will operate. Selecting one of three gains with one input308may be accomplished by connecting the gain control input308to a common voltage, e.g., grounding or logic low, for a first gain; to positive supply voltage, e.g., VCC, VDD, or logic high, for a second gain; and no connection, e.g., floating input, for a third gain. The three selectable gains may be configured for any three values and are correlated to three different control voltage levels at the gain control input308. For example the first gain may be 10, the second gain may be 50 and the third gain may be one (1). Any other three different gains may be used and are contemplated herein.

Referring toFIGS. 4aand4b, depicted are schematic circuit diagrams of a prior art non-inverting operational amplifier and a selectable gain amplifier, respectively, having voltage gains of one.FIG. 4ashows the circuit connections required to configure the operational amplifier102to have a gain of one.FIG. 4bshows the selectable gain amplifier302configured for the third gain. For this example the third gain may be defined as one within the amplifier302. Thus, the selectable gain amplifier302may be used with existing printed circuit boards by just leaving the resistor R0off of the printed circuit board.

Referring toFIGS. 5aand5b, depicted are schematic circuit diagrams of a prior art non-inverting operational amplifier and a selectable gain amplifier, respectively, having voltage gains of A.FIG. 5ashows the circuit connections required to configure the operational amplifier102to have a gain of A.FIG. 5bshows the selectable gain amplifier302configured for the second gain. For this example the second gain may be defined as A within the amplifier302. Thus, the selectable gain amplifier302may be used with existing printed circuit boards by just leaving resistors R1and R2off of the printed circuit board and put a jumper or conductive bridge in place of resister R2.

Referring toFIGS. 6aand6b, depicted are schematic circuit diagrams of a prior art non-inverting operational amplifier and a selectable gain amplifier, respectively, having voltage gains of B.FIG. 6ashows the circuit connections required to configure the operational amplifier102to have a gain of B.FIG. 6bshows the selectable gain amplifier302configured for the first gain. For this example the first gain may be defined as B within the amplifier302. Thus, the selectable gain amplifier302may be used with existing printed circuit boards by just leaving resistors R1and R2off of the printed circuit board and applying Vcc, Vdd, or logic high to the G input308.

Referring toFIG. 7, depicted is a schematic circuit diagram of another specific embodiment of a selectable gain amplifier having a voltage gain controlled by a digital device. The gain control input308of the selectable gain amplifier302is coupled to a digital device710. The digital device710drives the gain control input308, for example but not limited to, with a output712that is tri-state. However, any type output712that can drive a load to a logic high, logic low and be put into a high impedance may be used in this specific embodiment. For example, a first gain may be selected by logic low, a second gain may be selected by logic high, and a third gain selected by a high impedance, e.g., output712disconnected. The three selectable gains may be configured for any three values and are correlated to the two different logic levels and the high impedance at gain control input308. The digital device may be, for example but not limited to, a digital processor, microcontroller, microprocessor, application specific integrated circuit (ASIC), programmable logic array (PLA), and digital signal processor (DSP). The selectable gain amplifier and digital device may be enclosed in an integrated circuit and used in a mixed signal (both analog and digital) system.

Referring toFIG. 8, depicted is a schematic integrated circuit package pin-out diagrams of prior art operational amplifiers and corresponding selectable gain amplifiers. Standard pin-out integrated circuit packages may be used to package the selectable gain amplifier(s). As shown inFIG. 8, what used to be the −IN pins of the prior art packages are now gain control inputs, G, for the specific embodiments described herein. By using these standard integrated circuit packages and pin-outs with the selectable gain amplifier(s) as described herein, existing printed circuit board designs may be retained and a reduction of components (resistors) realized.

Referring toFIG. 9, depicted is a schematic integrated circuit package pin-out diagrams of a prior art quad operational amplifiers and corresponding selectable gain amplifiers, and other specific embodiments of selectable gain amplifier integrated circuit packaging. As shown inFIG. 9, what used to be the −IN pins of the prior art packages are now gain control inputs, G, for the specific embodiments described herein. By using these standard integrated circuit packages and pin-outs with the selectable gain amplifier(s) as described herein, existing printed circuit board designs may be retained and a reduction of components (resistors) realized.

The invention, therefore, is well adapted to carry out the objects and attain the ends and advantages mentioned, as well as others inherent therein. While the invention has been depicted, described, and is defined by reference to exemplary embodiments of the invention, such a reference does not imply a limitation on the invention, and no such limitation is to be inferred. The invention is capable of considerable modification, alternation, and equivalents in form and function, as will occur to those ordinarily skilled in the pertinent arts and having the benefit of this disclosure. The depicted and described embodiments of the invention are exemplary only, and are not exhaustive of the scope of the invention. Consequently, the invention is intended to be limited only by the spirit and scope of the appended claims, giving full cognizance to equivalents in all respects.