Techniques for external control of an amplifier's gain

Abstract

Amplifier circuit with programmable gain, featuring the following: at least one device pin (208A) designed to be coupled to an external gain adjustment resistor component (RG); a resistor component chain (202) comprising several resistor components (206A-206H); a comparator chain (204) with several comparator circuits (U1-U8), wherein the several comparator circuits (U1-U8) have the following: first inputs, which are coupled in such a way that they receive voltages generated by corresponding components of the multiple resistors; and second inputs that are coupled in such a way that they receive a voltage applied to at least one device pin (208A); a logic circuit (210) with multiple inputs coupled to corresponding outputs of the multiple comparator circuits (U1-U8); and an amplifier component that is adjustable by the logic circuit (210) based on outputs of the multiple comparator circuits (U1-U8), wherein the logic circuit (210) is configured to adjust the gain of the amplifier component based on a comparison between the voltages from the resistor component chain (202) and the voltage applied to the at least one device pin (208A).

Description

AREA OF REVELATION

[0001] This document concerns amplifier circuits in general, but not exclusively, and in particular amplifier circuits with programmable gain. BACKGROUND

[0002] Amplifiers can amplify a signal property, such as current, voltage, power, another signal property, or a combination thereof, of an incoming signal, such as an electrical signal. One type of amplifier is a programmable gain amplifier. A programmable gain amplifier may have adjustable resistors in a feedback path (from an amplifier output to an amplifier input), an input path (from an input terminal to the amplifier input), or both, to achieve varying gain levels.

[0003] Some conventional amplifiers use a single external resistor to adjust the gain. The resistance value of this external resistor is used in the gain equation, which defines the amplifier's gain. Tolerances and inaccuracies in the external resistor can directly affect the overall performance of the amplifier.

[0004] US 2010 / 0194620A1 describes a parallel analog-to-digital converter (ADC) with a comparator chain, a reference voltage ladder, and an encoder for converting thermometer codes into binary codes. To improve conversion accuracy, a mechanism for detecting and correcting so-called "bubbles" (errors in the thermometer encoding) is employed, and the clock ratios for sampling and comparison operations can also be dynamically adjusted. The circuit is thus used exclusively for digitizing analog input signals while minimizing encoding errors.

[0005] US Patent 10,103,742 B1 relates to a multi-stage hybrid analog-to-digital converter (ADC) that combines a successive approximation register (SAR) stage and a flash ADC stage in a pipeline architecture. The goal is to combine high resolution, high speed, and low power consumption in a single system. The first and last stages consist of SAR ADCs, which operate with low energy and area efficiency, while the middle stage is a fast flash ADC that handles time-critical conversions.

[0006] DE 10 2015 117 109 A1 describes a device and a method for digitally controlling the output amplitude of an analog sensor signal. The invention comprises an analog main signal path that amplifies and outputs a sensor signal, and a digital control circuit that generates a digital control signal to compensate for amplification errors or ratiometric behavior. The amplification is adjusted, among other things, by digitally controllable resistor elements within an amplifier. BRIEF SUMMARY OF THE INVENTION

[0007] This disclosure describes, among other things, techniques for setting the gain of an amplifier circuit where the external resistance of the amplifier circuit is used to determine a selectable internal gain setting. This approach contrasts with other approaches where a resistance value of the external resistor is used in the actual gain equation that determines the gain of the amplifier circuit. Here, a voltage across the external resistor can be compared to an on-chip reference and then used to program the desired gain. These techniques can reduce or eliminate the need for an exact external resistor and can enable significant improvements in initial gain accuracy and gain drift for existing boards and / or systems with just a change to the bill of materials.

[0008] In some aspects, this disclosure relates to an amplifier circuit according to the invention as claimed in claim 1.

[0009] In some aspects, this disclosure further relates to a method according to the invention for operating an amplifier circuit with programmable gain according to claim 10.

[0010] This overview is intended to provide a summary of the subject matter of the present patent application. It is not intended to provide an exclusive or exhaustive explanation of the invention. The detailed description is included to provide further information about the present patent application. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] In the drawings, which are not necessarily drawn to scale, the same numbers may describe similar components in different views. The same numbers with different letter suffixes may represent different instances of similar components. The drawings generally illustrate, by way of example but not as a limitation, various embodiments discussed in this document. Fig. Figure 1 is an example of an amplifier circuit. Fig. Figure 2 is an example of an amplifier circuit with programmable gain that can implement various techniques of this revelation. Fig. Figure 3 is another example of an amplifier circuit with programmable gain that can implement various techniques of this revelation. Fig. Figure 4 is another example of an amplifier circuit with programmable gain that can implement various techniques of this revelation. Fig. Figure 5 is another example of an amplifier circuit with programmable gain that can implement various techniques of this revelation. Fig. Figure 6 is another example of an amplifier circuit with programmable gain that can implement various techniques of this revelation. Fig. Figure 7 is a flowchart of an example of a method for operating an amplifier circuit with programmable gain. DETAILED DESCRIPTION

[0012] Many conventional amplifier circuits use a single external resistor to adjust the gain of the amplifier circuit. The resistance value of the external resistor is used in the actual gain equation, which determines the gain of the amplifier circuit. The tolerances and inaccuracies of the external resistor can directly affect the overall performance of the amplifier circuit.

[0013] Some amplifier circuits, such as programmable gain instrumentation amplifiers (PGIAs), can achieve excellent gain accuracy because all gain-adjusting resistors are integrated on the chip. Unfortunately, these PGIAs may not have the same packages and pinouts as their predecessors, and simpler approaches that provide one or two on-chip gains may lack flexibility.

[0014] This disclosure describes, among other things, techniques for setting the gain of an amplifier circuit where the external resistance of the amplifier circuit is used to determine a selectable internal gain setting. This approach contrasts with other approaches where a resistance value of the external resistor is used in the actual gain equation that determines the gain of the amplifier circuit. Here, a voltage across the external resistor can be compared to an on-chip reference and then used to program the desired gain. These techniques can reduce or eliminate the need for an exact external resistor and can enable significant improvements in initial gain accuracy and gain drift for existing boards and / or systems with just a change to the bill of materials.

[0015] Fig. Figure 1 is an example of an amplifier circuit. Amplifier circuit 100 is an example of a programmable gain instrumentation amplifier (PGIA) circuit, comprising three operational amplifiers 102-106 implemented with a network of high-quality on-chip resistors. Two of the operational amplifiers, namely amplifiers 102 and 104, can form an input amplifier section and can be used to provide the user with high-impedance differential inputs while simultaneously providing gain. The third amplifier, 106, can be configured as a differential amplifier and is used to convert the amplified differential signal into a ground-referenced buffered output.

[0016] The final gain of the input amplifier section can be determined by the ratio of on-chip resistors RF to the discrete (external) off-chip resistor RG, given by the gain equation (1 + (2*RF / RG)). Although the approach of Fig. While it may offer a useful way to provide user-adjustable gain, it entails a practical limitation on the accuracy of that gain.

[0017] Gain inaccuracy can be caused by a lack of correlation between the on-chip resistors RF and the external resistor RG. While the RF resistors may be trimmed to an absolute value within approximately 0.1%, any tolerance in the external resistor RG can further impair the gain error. A lack of correlation between the temperature coefficients of the RF resistors and the RG resistor can also cause the amplifier circuit's gain to change with temperature. Initial gain error and gain drift specifications in datasheets reflect the performance of the on-chip components and assume the use of an ideal external resistor RG.In practice, the tolerance and temperature coefficient of the external resistance RG limit performance, and resistors with tighter tolerances and lower temperature coefficients tend to be more expensive and less available.

[0018] Instead of requiring the user to provide the external resistor RG, the resistor RG is integrated into some PGIAs to track the resistors RF and achieve significantly better gain accuracy. While effective, this can be limiting for simpler offerings that provide only one or two gain settings. More recent PGIA designs represent an improvement in flexibility, as they can provide a much larger number of discrete gains while still achieving the gain accuracy benefit of integrating all the resistors. Unfortunately, these PGIAs do not fit within the footprint of standard instrumentation amplifiers.

[0019] As described below, various techniques of this revelation can provide a way to adapt modern amplifier designs to standard footprints, thereby enabling improved gain accuracy in existing systems with a change to the bill of materials. A voltage across the external resistor RG, e.g., an inexpensive standard component, can be compared to an on-chip reference and then used to program the desired gain, for example, by using a logic circuit, such as one incorporating an encoder, to control the gain selection of the amplifier circuit.In this way, the external resistor RG is used to decide which gain setting to use, instead of being used as part of the gain equation to determine the gain, and all analog gain setting resistors are integrated on the chip, thus enabling a significant improvement in gain accuracy.

[0020] Fig. Figure 2 is an example of a programmable gain amplifier circuit that can implement various techniques of this disclosure. The programmable gain amplifier circuit 200 can have a resistive component chain 202 coupled to a comparator chain 204. The resistive component chain 202 can have multiple resistive components, e.g., a resistive voltage divider, as in the non-restrictive example of Figure 2. Fig. 2 as eight resistor components 206A-206H. Other component chains may have more than eight resistor components or fewer than eight resistor components. The comparator chain 204 may have multiple comparator circuits, as shown in the non-restrictive example of Fig. Figure 2 shows comparator circuits U1-U8. Other comparator chains may have more than eight comparators or fewer than eight comparators.

[0021] The amplifier circuit 200 with programmable gain can have one or more device pins 208A, 208B which can be coupled to an external gain-adjusting resistor component RG, such as a resistor. By using various techniques of this disclosure, the comparator circuits U1-U8 of the comparator chain 204 can compare a voltage generated across the external gain-adjusting resistor component RG with voltages generated across corresponding voltages of the multiple resistor components, and a logic circuit 210 can adjust a gain of the amplifier circuit with programmable gain based on the outputs of the multiple comparator circuits.

[0022] In particular, the comparator circuits U1-U8 can have first inputs, such as non-inverting input terminals, which are coupled to receive voltages generated by corresponding of the several resistor components, and second inputs, such as inverting input terminals, which are coupled to receive voltages generated at a node 224, such as at the external gain-adjusting resistor component RG.

[0023] In some examples, the comparator chain 204 is configured to generate a thermometer code. The resistive component chain 202, e.g., the resistive voltage divider, can operate via a source 220, for example, a voltage source or a current source, coupled to node 222, to supply the reference voltages to the non-inverting input terminals of comparators U1-U8 of the comparator chain 204 and to node 224. The voltage at node 224 is coupled to, or applied to, the inverting input terminals of comparators U1-U8 of the comparator chain 204.

[0024] For example, the reference voltage for each comparator in comparator chain 204 is one least significant bit (LSB) higher than the reference voltage for the comparator immediately below it. The outputs of comparators U1-U8 can collectively provide a "thermometer code" corresponding to the magnitude of the external gain-adjustment resistor component RG.

[0025] The logic circuit 210 can have multiple inputs, such as inputs OUT1-OUT8 in Fig. 2, which are coupled to corresponding outputs of the comparator circuits U1-U8. The logic circuit 210 can generate a control signal based on the outputs of the comparator circuits U1-U8 and an output 212 of the logic circuit 210 to set a gain of the amplifier circuit 200 with programmable gain. For example, the logic circuit 210 can generate a 3-bit digital output control signal A[2:0] to control one or more switches 214 for selectively coupling one or more resistor components 216 with an amplifier component 218, such as coupling one or more resistor components 216 in a negative feedback configuration around the amplifier component 218. The one or more selected resistor components can program the gain of the amplifier component 218.

[0026] In some examples, the logic circuit 210 may include an encoder circuit 226 for converting the thermometer code into a binary code. For example, the encoder circuit 226 may include OR gates configured and arranged to receive the thermometer code and output a binary code.

[0027] In some examples, if a higher supply voltage VCC is used, for example greater than 5 V, it may be desirable to include a level conversion circuit 228 to convert the level of the output of the logic circuit 210, since the resistor component chain 202 can float with the input.

[0028] Fig. Figure 3 is another example of a 300 amplifier circuit with programmable gain, which can implement various techniques of this revelation. Many of the components in Fig. 3 are the ones above in relation to Fig. The two described above are similar and will not be described in detail again for the sake of clarity.

[0029] In the Fig. The example shown in 3 can be source 220 from Fig. 2. A first current source 302, coupled to a first end of the resistor component chain 202, and a second current source 304, coupled to the external gain-adjusting resistor component RG, are provided. The first current source 302 and the second current source 304 can generate substantially identical known currents that can be fed into the resistor component chain 202 and the external gain-adjusting resistor component RG.

[0030] As described above, the voltage across the external gain-adjustment resistor RG can be compared by the comparators of comparator chain 204 with reference voltages generated across the resistor components of resistor chain 202. The logic circuit 210 can encode the outputs of comparators U1-U8 to drive a gain selection of the programmable gain amplifier circuit 300. In this way, the external gain-adjustment resistor RG is used to determine which gain setting to use, rather than being part of the gain equation, and all analog gain-adjustment resistors are integrated on the chip, resulting in a significant improvement in gain accuracy.

[0031] Fig. Figure 4 is another example of a programmable gain amplifier circuit 400 that can implement various techniques of this disclosure. The programmable gain amplifier circuit 400 can have at least two amplifier circuits. For example, the programmable gain amplifier circuit 400 in the non-limiting example shown can have a first amplifier component 402, a second amplifier component 404, and a third amplifier component 406. The third amplifier component is an example of amplifier component 218 from Figure 4. Fig. 2 and Fig. 3. In some examples, the third amplifier component 406 can be arranged in a negative feedback configuration.

[0032] In some examples, the amplifier circuit 400 with programmable gain can be arranged in a configuration of an instrumentation amplifier with programmable gain. In some examples, the first amplifier component 402 and the second amplifier component 404 can form part of an input stage, and the third amplifier component 406 can form part of a differential stage, with inputs of the differential stage coupled to outputs of the input stage.

[0033] As in Fig. As can be seen in section 4, various switches 214 can be controlled using digital outputs A3-A1 of a logic circuit, such as the logic circuit 210 of Fig. 2. Based on the outputs of the several comparator circuits, resistor components 216 of different resistance values ​​are coupled to adjust the gain of the amplifier circuit 400 with programmable gain. It is understood that the resistance values ​​of the resistor components 216 are non-limiting values ​​and are used for illustrative purposes only.

[0034] Fig. Figure 5 is another example of a programmable gain amplifier circuit 500 that can implement various techniques of this disclosure. In some examples, the programmable gain amplifier circuit 500 can have an amplifier component 502 with a differential input for receiving a differential input signal at its non-inverting input terminal and its inverting input terminal. In some such examples, the amplifier component 502 can have a differential output, as shown in Figure 5. Fig. 5 shown, and thus be fully differential. In other examples, amplifier component 502 may have a single-pole output terminal. Amplifier component 502 is an example of amplifier component 218 of Fig. 2. In some examples, the amplifier component 502 can be arranged in a negative feedback configuration.

[0035] As in Fig. As can be seen in section 5, various switches 214 can be controlled using a logic circuit, such as the logic circuit 210 from Fig. 2, generated digital control signal A[N:0], which is based on the outputs of the multiple comparator circuits, couple resistor components 216 of different resistance values ​​to set a gain of the amplifier circuit 500 with programmable gain.

[0036] Fig. Figure 6 is another example of an amplifier circuit 600 with programmable gain, which can implement various techniques of this disclosure. In some examples, the amplifier circuit 600 can include an amplifier component 602 arranged in an operational amplifier configuration. The amplifier component 602 is an example of the amplifier component 218 of Fig. 2. In some examples, the amplifier circuit 602 can be arranged in a negative feedback configuration.

[0037] As in Fig. As can be seen in section 6, various switches 214 can be controlled using a logic circuit, such as the logic circuit 210 from Fig. 2, generated digital control signal A[N:0], which is based on the outputs of the multiple comparator circuits, couple resistor components 216 of different resistance values ​​to set a gain of the amplifier circuit 600 with programmable gain.

[0038] Fig. Figure 7 is a flowchart of a procedure 700 for operating an amplifier circuit with programmable gain. The in Fig. The circuits shown in Figures 2-6 can be used to implement Method 700.

[0039] In block 702, the method 700 can involve generating multiple voltages across corresponding resistor components of a resistor component chain. For example, the first current source 302 of Fig. 3 several voltages at corresponding resistor components 206A-206H of the resistor component chain 202 of Fig. 3 generate.

[0040] In block 704, the procedure 700 can involve comparing corresponding voltages of several voltages with a reference voltage generated at an external gain-adjustment resistor component. For example, the comparators U1-U8 of comparator chain 204 can be Fig. 3. Compare the corresponding voltages generated at the resistance components of the resistance component chain 202 with a reference voltage generated at the gain adjustment resistance component RG.

[0041] In block 706, procedure 700 can determine a code based on comparison. For example, logic circuit 210 of Fig. 3. Determine a thermometer code based on the comparison.

[0042] In block 708, procedure 700 can generate a control signal based on the code. For example, logic circuit 210 of Fig. 3. Generate a digital output control signal based on the code.

[0043] In block 710, the method 700 can control, based on the control signal, at least one switch for connecting a resistive component to adjust the gain of the amplifier circuit with programmable gain. For example, the logic circuit 210 can control one or more switches 214 to selectively couple one or more resistive components 216 with an amplifier component 218, such as coupling one or more resistive components 216 in a negative feedback configuration around the amplifier component 218. The one or more selected resistive components can program the gain of the amplifier component 218.

[0044] In this document, the terms "a" or "an" are used, as is customary in patent documents, to include one or more than one, irrespective of any other instances or uses of "at least one" or "one or more". In this document, the term "or" is used to refer to a non-exclusive "or", so that "A or B" includes "A but not B", "B but not A", and "A and B" unless otherwise specified. In this document, the terms "including" and "in which" are used as the equivalents of the respective terms "including" and "whereby" in plain English.Furthermore, the terms "including" and "comprising" in the following claims are open expressions, meaning that a system, device, article, composition, formulation, or process that includes elements in addition to those listed after such a term in a claim will still be considered to fall within the scope of protection of that claim. Additionally, in the following claims, the terms "first," "second," and "third," etc., are used merely as designations and are not intended to be interpreted as numerical specifications for their objects.

[0045] The process examples described here may be at least partially machine- or computer-implemented. Some examples may include a computer-readable or machine-readable medium encoded with instructions capable of configuring an electronic device to perform processes as described in the examples above. An implementation of such processes may include code such as microcode, assembly language code, code of a higher-level programming language, or the like. Such code may contain computer-readable instructions for performing various processes. The code may form parts of computer program products. Furthermore, in one example, the code may be stored tangible on one or more volatile, non-perishable, or non-volatile tangible computer-readable media, such as during execution or at other times.Examples of these tangible, computer-readable media include hard disks, removable magnetic disks, removable optical disks (e.g., compact discs and digital video discs), magnetic cassettes, memory cards or sticks, random access memory (RAMs), read-only memory (ROMs), and the like.

[0046] The above description is intended to be illustrative and not limiting. For example, the examples described above (or one or more aspects thereof) may be used in combination with one another. Other embodiments may be used, for instance, by a person skilled in the art after reviewing the above description. Furthermore, various features may be grouped together in the above detailed description to streamline the disclosure. This should not be interpreted as implying that an unclaimed disclosed feature is essential to any claim. Rather, the subject matter of the invention may consist of fewer than all features of a particular disclosed embodiment.Accordingly, the following claims are hereby included in the detailed description as examples or embodiments, each claim constituting a separate embodiment on its own, and it is intended that such embodiments may be combined with one another in various combinations and permutations. The scope of protection of the invention should be determined with reference to the attached claims together with the full scope of protection of equivalents to which such claims entitle.

Claims

[1] Amplifier circuit with programmable gain, comprising the following: at least one device pin (208A) designed to be coupled to an external gain adjustment resistor component (RG); a resistor component chain (202) comprising several resistor components (206A-206H); a comparator chain (204) with several comparator circuits (U1-U8), wherein the several comparator circuits (U1-U8) have the following: first inputs, which are coupled in such a way that they receive voltages generated by corresponding components of the multiple resistors; and second inputs that are coupled in such a way that they receive a voltage applied to at least one device pin (208A); a logic circuit (210) with multiple inputs coupled to corresponding outputs of the multiple comparator circuits (U1-U8); and an amplifier component that is adjustable by the logic circuit (210) based on outputs of the multiple comparator circuits (U1-U8), wherein the logic circuit (210) is configured to adjust the gain of the amplifier component based on a comparison between the voltages from the resistor component chain (202) and the voltage applied to the at least one device pin (208A). [2] Amplifier circuit with programmable gain according to claim 1, wherein the comparator chain (204) is configured to generate a thermometer code. [3] Amplifier circuit with programmable gain according to claim 2, wherein the logic circuit (210) is configured to convert the thermometer code into a binary code. [4] Amplifier circuit with programmable gain according to one of claims 1 to 3, wherein the logic circuit (210) comprises a level conversion circuit (228) for adjusting a voltage level of an output of the logic circuit (210). [5] Amplifier circuit with programmable gain according to any one of claims 1 to 4, wherein the amplifier component comprises a first and a second amplifier component (402, 404) arranged in an instrumentation amplifier configuration. [6] Amplifier circuit with programmable gain according to any one of claims 1 to 5, wherein the amplifier component is an amplifier component having a differential input for receiving a differential input signal. [7] Amplifier circuit with programmable gain according to claim 6, wherein the amplifier component further comprises a differential output for generating a differential output signal. [8] Amplifier circuit with programmable gain according to any one of claims 1 to 7, wherein the amplifier component is an amplifier component arranged in a negative feedback configuration. [9] Amplifier circuit with programmable gain according to any one of claims 1 to 8, comprising the following: a first current source (302) coupled to a first end of the resistor component chain (202); and a second power source (304) coupled to the at least one device pin (208A), wherein the second inputs of the multiple comparator circuits (U1-U8) are coupled such that they receive the voltage generated by an external gain setting resistor component (RG) and the second current source, applied to at least one device pin (208A). [10] Method for operating an amplifier circuit with programmable gain, wherein the method comprises: Generating multiple voltages across corresponding resistance components (206A-206H) of a resistance component chain (202); Comparing corresponding voltages of the several voltages with a reference voltage generated at an external gain adjustment resistor component (RG) by comparators (U1-U8) of a comparator chain (204) comparing corresponding voltages of the several voltages generated at the resistor components of the resistor component chain (202) with a reference voltage generated at the gain adjustment resistor component (RG); Determining a code based on comparison; Generating a control signal based on the code; and Control, based on the control signal, of at least one switch (214) to connect another resistor component (216) to adjust the gain of an amplifier component of the amplifier circuit with programmable gain. [11] Method according to claim 10, wherein determining the code based on the comparison comprises: Determining a thermometer code. [12] The method of claim 11, comprising: Converting the thermometer code into a binary code. [13] Method according to any one of claims 10 to 11, comprising the following: Adjusting a voltage level of an output of a logic circuit (210).

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