Modular signal source with offset removal function

Abstract

This application relates to two modular signal sources with offset removal capabilities. Signal sources are among the most common and basic types of general-purpose electronic test instruments. Other general-purpose electronic test instruments, such as network analyzers and impedance spectroscopy analyzers, also include signal sources. A typical modular signal source includes: a basic signal source circuit, a gain adjustment circuit, a bias circuit, a microcontroller, and a host computer. The challenge with modular signal sources is the susceptibility to output offset, i.e., a large difference between the actual output bias value and the set bias value. Furthermore, it seems impossible to resolve this offset problem using analog circuits alone. The solution in this application pre-detects the output offset value and stores it as an offset compensation value on the microcontroller or host computer. This offset is then subtracted from the set ideal bias value, thereby significantly reducing the amount of output offset.

Description

Technical Field

[0001] This application relates to two modular signal sources with offset removal capabilities.

[0002] Signal sources are one of the most common and basic types of general-purpose electronic test instruments. Some other general-purpose electronic test instruments, such as network analyzers and impedance spectroscopy analyzers, also include signal sources. Signal sources can be designed to output sine waves, triangular waves, sawtooth waves, or even arbitrary waveforms as needed.

[0003] The modular signal source in this application refers to an instrument with signal source function formed by a signal source circuit module and a personal computing device. Here, the personal computing device refers to a regular PC, mobile phone, PAD, etc., which are collectively referred to as a host computer in this application. The advantages of a modular signal source are: ease of development and portability. Background Technology

[0004] A typical modular signal source includes: a basic signal source circuit, a gain adjustment circuit, a bias circuit, a microcontroller, and a host computer. The basic signal source circuit is often an integrated circuit that generates a source signal of a certain type, the frequency of which can be set by the microcontroller, and its amplitude is generally fixed. The gain adjustment circuit is an amplifier circuit whose gain is controlled by the microcontroller through programming to achieve signal outputs of different amplitudes. The bias circuit includes a digital-to-analog converter (DAC) and a summing circuit. The microcontroller controls the DAC output to set a bias value, which is then superimposed onto the output signal by the summing circuit as the final output.

[0005] The challenge of the modular signal source described above is that it is prone to output offset, meaning that the actual output bias value is likely to differ from the set bias value. This is because the basic circuitry of the signal source has bias or offset issues, and the gain adjustment and summing circuits also exhibit varying degrees of offset. In particular, the multiple gain levels of the gain adjustment circuit correspond to different degrees of offset voltage, making it impossible to resolve the offset problem using the analog circuitry itself. Summary of the Invention

[0006] Purpose of the invention.

[0007] A solution is proposed that has an offset removal function for modular signal sources, so that the actual output bias of the modular signal source is consistent with the set bias value. When the set bias value is 0, the actual output bias value is also close to 0.

[0008] Technical solution.

[0009] A modular signal source with offset removal function includes a basic signal source circuit, a gain adjustment circuit, a bias circuit, a microcontroller, and a host computer. Its features include: (1) the basic signal source circuit generates a source signal of a certain type, the frequency of which is set by the microcontroller, and its amplitude is fixed; (2) the gain adjustment circuit is an amplifier circuit whose gain is controlled by the microcontroller through programming, amplifying or reducing the signal generated by the basic signal source circuit; (3) the bias circuit includes a digital-to-analog converter (DAC) and a summing circuit, whereby the microcontroller controls the DAC to output a bias value, which is then superimposed onto the output signal of the gain adjustment circuit by the summing circuit to generate the final signal output; (4) the microcontroller controls the DAC to output a bias value whose magnitude is set by the host computer. The ideal bias value of the output minus the offset compensation value stored in the microcontroller: (5) The method for determining the offset compensation value is to first set the bias value of the DAC output controlled by the microcontroller to 0 in the initial state of the modular signal source. At this time, the actual output offset or actual bias value of the signal source is the offset compensation value; (6) Pre-measure the offset compensation value of each gain of the signal source and store it in the ROM memory of the microcontroller for use during corresponding compensation; (7) For different modular signal sources, due to the individual differences in circuit devices, the output offset also has individual differences. Therefore, a set of personalized offset compensation values ​​can be established for each modular signal source and stored in the ROM memory of its microcontroller for use during corresponding compensation.

[0010] A modular signal source with offset removal function includes a basic signal source circuit, a gain adjustment circuit, a bias circuit, a microcontroller, and a host computer. The characteristics are: (1) The basic signal source circuit generates a source signal of a certain type, the frequency of which is set by the microcontroller, and its amplitude is fixed; (2) The gain adjustment circuit is an amplifier circuit whose gain is controlled by the microcontroller through programming, amplifying or reducing the signal generated by the basic signal source circuit; (3) The bias circuit includes a digital-to-analog converter (DAC) and a summing circuit. The microcontroller controls the DAC to output a bias value, which is then superimposed onto the output signal of the gain adjustment circuit through the summing circuit to generate the final signal output; (4) The bias value output by the DAC controlled by the microcontroller originates from the host computer, and its magnitude is the ideal bias value set by the host computer for output. The offset compensation value is subtracted from the offset compensation value stored in the host computer: (5) The method for determining the offset compensation value is that, in the initial state of the modular signal source, the host computer first sets the ideal bias value to be output and the offset compensation value to 0. At this time, the actual output offset or actual bias value of the signal source is the offset compensation value; (6) The offset compensation values ​​of each gain of the signal source are measured in advance and stored in a certain path of the host computer's hard disk as a configuration file for the corresponding compensation; (7) For different modular signal sources, due to the individual differences in circuit devices, the output offset also has individual differences. Therefore, a set of personalized offset compensation values ​​can be established for each individual signal source and stored in the host computer's hard disk as a configuration file for the host computer to call when making corresponding compensation.

[0011] The main difference between the two schemes lies in the storage location of the offset compensation value. The former stores it in the microcontroller's ROM, while the latter stores it in the host computer's hard drive. In the former, the host computer only provides the microcontroller with the set ideal bias value to be output. The microcontroller subtracts the offset compensation value and sends the difference to the DAC output. In the latter, the host computer performs the operation of subtracting the offset compensation value from the set ideal bias value to be output. The host computer then provides the difference to the microcontroller, which does not perform the subtraction operation again and sends the difference directly to the DAC output.

[0012] Beneficial effects.

[0013] In the following section on embodiments, a signal source with offset removal function as described in this application was fabricated and tested. First, the output offset values ​​corresponding to different signal gains were measured in the initial state where the ideal output bias value was set to 0V and the offset compensation value was also set to 0V, as shown in column 4 of Table 1. Then, the offset compensation value was reset to the measured output offset value, as shown in column 5 of Table 1. Finally, the output offset value after resetting the offset compensation was measured, as shown in column 6 of Table 1.

[0014] The above tests demonstrate that the technical solution of this application is feasible. Through compensation, the output misalignment value can be greatly reduced by at least one order of magnitude, thus achieving substantial progress.

[0015] Table 1. Test and compensation results of output offset under different signal gains.

[0016] Attached Figure Description

[0017] Figure 1 The diagram shows a typical modular signal source block diagram belonging to this application. In the diagram, ∑ refers to the summation circuit, which, together with the analog-to-digital converter (DAC), forms a bias circuit.

[0018] Figure 2 This application presents a modular signal source block diagram. In the diagram, ∑ refers to the summation circuit, which, together with the analog-to-digital converter (DAC), forms a bias circuit. The offset compensation value is stored in the microcontroller, and a subtraction operation is performed between the ideal bias setting value and the offset compensation value.

[0019] Figure 3 This application presents another modular signal source block diagram. In the diagram, ∑ refers to the summation circuit, which, together with the analog-to-digital converter (DAC), forms the bias circuit. The offset compensation value is stored in the host computer, and a subtraction operation is performed between the ideal bias setting value and the offset compensation value.

[0020] Figure 4 The software interface diagram of the signal source output signal in this embodiment is shown. In the diagram, BiasVoltage = 0V is the ideal bias value set by the signal source, and the mean value -2.561E-3 (unit V) is the measured offset value or measured bias value. At this time, the offset is not compensated, and the offset compensation value is set to 0.

[0021] Figure 5 The software interface diagram of the signal source output signal in this embodiment is shown. In the diagram, BiasVoltage = 0V is the ideal bias value set by the signal source, and the mean value -2.091E-5 (unit V) is the measured offset value or measured bias value. At this time, offset compensation is performed, and the offset compensation value is set to -2.561E-3 (unit V). Detailed Implementation

[0022] Example. A modular signal source with offset removal function includes a basic signal source circuit, a gain adjustment circuit, a bias circuit, a microcontroller, and a host computer. The ADI9833 integrated circuit is selected as the basic signal source circuit; the PGA281 programmable gain amplifier is selected to build the gain adjustment circuit; the DAC8551 is selected as the digital-to-analog converter (DAC) in the bias circuit; the OPA320 is selected to build the summing circuit in the bias circuit; the STM32 is selected as the microcontroller; and a general-purpose PC is selected as the host computer. Communication between the microcontroller and the host computer is achieved using a USB-to-serial chip CH343G. The ADI9833 signal source basic circuit generates a source signal of one type, the frequency of which is set by the STM32 microcontroller. A gain adjustment circuit is built based on the PGA281, offering 11 gain levels: 1 / 8, 1 / 4, 1 / 2, 1, 2, 4, 8, 16, 32, 64, and 128. Its configuration is controlled by the STM32 microcontroller programmable, amplifying or attenuating the signal generated by the basic circuit. The bias circuit includes a DAC8551 and an OPA320 summing circuit. The STM32 microcontroller controls the DAC8551 to output a bias value, which, along with the PGA281's output signal, is sent to the OPA320 summing circuit. The bias value controlled by the microcontroller for the DAC output is derived from a setting in the host computer; its magnitude is the ideal output bias value set by the host computer minus the value stored in the host computer. The offset compensation value is determined by setting both the ideal bias value and the offset compensation value to 0 in the initial state of the modular signal source. The measured actual output offset, or actual bias value, is then used as the offset compensation value. Eleven offset compensation values ​​are pre-measured for each gain of the signal source, as shown in column 4 of Table 1. These values ​​are saved in a specific path on the host computer's hard drive as a configuration file for use under different signal gains. Due to individual differences in circuit components, the output offset also varies for different modular signal sources. Therefore, a set of personalized offset compensation values ​​is created for each signal source and saved on the host computer's hard drive as a configuration file for use under different signal gains. In implementation, the basic signal source circuit, gain adjustment circuit, bias circuit, microcontroller, and USB-to-serial chip CH343G are fabricated on the same circuit board, communicating with a regular PC via USB. Ultimately, a signal source with offset compensation functionality is achieved.

Claims

1. A modular signal source with offset removal function, comprising a basic signal source circuit, a gain adjustment circuit, a bias circuit, a microcontroller, and a host computer, characterized in that, (1) The basic circuit of the signal source generates a type of source signal whose frequency is set by the microcontroller and whose amplitude is fixed. (2) Gain adjustment circuit is an amplifier circuit whose gain is controlled by microcontroller programming to amplify or reduce the signal generated by the basic circuit of the signal source; (3) Bias circuit includes a digital-to-analog converter (DAC) and a summing circuit. The microcontroller controls the DAC to output a bias value, which is then superimposed on the output signal of the gain adjustment circuit through the summing circuit to generate the final signal output; (4) The microcontroller controls the DAC to output a bias value, the size of which is the ideal bias value to be output set by the host computer minus the offset compensation value stored in the microcontroller; (5) The method for determining the offset compensation value is to first set the bias value of the DAC output by the microcontroller to 0 in the initial state of the modular signal source. At this time, the actual output offset value of the signal source measured is the offset compensation value; (6) The offset compensation value of each gain of the signal source is measured in advance and stored in the ROM memory of the microcontroller for use during corresponding compensation; (7) A set of personalized offset compensation values ​​is established for each modular signal source and stored in the ROM memory of its microcontroller for use during corresponding compensation.

2. A modular signal source with offset removal function, comprising a basic signal source circuit, a gain adjustment circuit, a bias circuit, a microcontroller, and a host computer, characterized in that, (1) The basic circuit of the signal source generates a type of source signal whose frequency is set by the microcontroller and whose amplitude is fixed. (2) The gain adjustment circuit is an amplifier circuit whose gain is controlled by the microcontroller programming to amplify or reduce the signal generated by the basic circuit of the signal source; (3) The bias circuit includes a digital-to-analog converter (DAC) and a summing circuit. The microcontroller controls the DAC to output a bias value, which is then superimposed on the output signal of the gain adjustment circuit by the summing circuit to generate the final signal output; (4) The bias value output by the DAC controlled by the microcontroller comes from the host computer. Its magnitude is the ideal bias value to be output set by the host computer minus the offset compensation value stored in the host computer; (5) The method for determining the offset compensation value is as follows: In the initial state of the modular signal source, the host computer first sets the ideal bias value and offset compensation value to be output to 0. At this time, the actual output offset value of the signal source is measured as the offset compensation value; (6) Pre-measure the offset compensation value of each gain of the signal source and save them in a certain path of the host computer's hard disk as a configuration file for the corresponding compensation call; (7) Establish a set of personalized offset compensation values ​​for each individual signal source and save them in the host computer's hard disk as a configuration file for the host computer to call when making corresponding compensation.

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