Linear isolation amplifier and method for self-calibration thereof

An amplifier circuit may include an isolated amplifier circuit, disposed on a high voltage side of the amplifier circuit, and arranged to generate an isolated output signal. The amplifier circuit may include a first optocoupler circuit, disposed to receive the isolated output signal from the isolated amplifier circuit and an output amplifier circuit, disposed on a low voltage side of the amplifier circuit, and coupled to receive an optical output signal from the optocoupler circuit. The amplifier circuit may also include a calibration circuit, coupled to the output amplifier circuit, to generate a calibration initiation signal, and a second optocoupler circuit, disposed to receive the calibration initiation signal, and to output a switch signal, wherein a reference voltage is output to the isolated amplifier circuit.

BACKGROUND

Field

Embodiments relate to the field of circuit protection devices, including noise filters.

Discussion of Related Art

Linear isolation circuits are known, such as linear optoisolators, also known as optocouplers. Known linear optoisolation circuitry includes optical emitters that generate radiant flux across a galvanically-isolated path. Receivers are provided that recover the initial analog signals across an electrically isolated barrier. This facilitates passing analog sense or control signals across electrically isolated circuits such as in power supply designs. Applications of optocouplers include use in linear isolation amplifiers and related circuitry. One feature of linear amplifiers based on optocouplers is the relation between input voltage VIN and output voltage VOUT, given by VOUT=VIN*K3 R2/R1, where R2 is the value of a resistor on the output side and R1 is the value of a resistor on the input side. K3 is a constant referred to as the transfer gain. Because optocoupler circuitry involves semiconductor materials, including light emitting diodes, as well as photodetectors, the properties of linear amplifiers using such circuitry depends upon the properties of the materials of optocouplers, as well as other circuit components. In practice, variation in properties among different optocoupler-based linear isolation amplifiers using nominally the same manufacturing process may cause substantial variation in the value of K3, the transfer gain. For example, K3 may vary by 10%, 20%, or 30% over different lots of optocouplers, so that an isolation amplifier design must accommodate this variation. In particular, when a customer wants a value of 1.0 for transfer gain, and the value of K3 varies above or below this value depending upon the optocoupler lot, resistance needs to be added or subtracted from the isolation amplifier circuit to achieve the value of 1. One manner of accommodating this variation is to alter R1 and R2 values in the linear amplifier circuitry, requiring resistors to be altered or swapped. Also, if K3 varies within a given linear amplifier circuit for some reason over time, there is no way to correct for this variation once the amplifier circuitry has been finalized.

In view of the above, the present embodiments are provided.

BRIEF SUMMARY

In some embodiments, an amplifier circuit is provided, including an isolated amplifier circuit, disposed on a high voltage side of the amplifier circuit, and arranged to generate an isolated output signal. The amplifier circuit may include a first optocoupler circuit, disposed to receive the isolated output signal from the isolated amplifier circuit and an output amplifier circuit, disposed on a low voltage side of the amplifier circuit, and coupled to receive an optical output signal from the optocoupler circuit. The amplifier circuit may also include a calibration circuit, coupled to the output amplifier circuit, to generate a calibration initiation signal, and a second optocoupler circuit, disposed to receive the calibration initiation signal, and to output a switch signal, wherein a reference voltage is output to the isolated amplifier circuit.

In another embodiment, a method of calibrating a linear isolation amplifier may include switching the linear isolation amplifier from an OFF state to an ON state. The method may include sending a signal to a calibration pin, to set the calibration pin in a low state for a predetermined interval, wherein a low voltage is set on a cathode of a calibration light emitting diode (LED), disposed on a low voltage side of the linear isolation amplifier, wherein the calibration LED generates a light signal. The method may also include receiving the light signal at a photodetector, disposed on a high voltage side of the linear isolation amplifier, wherein a switch signal is generated by the photodetector. The method may further include receiving the switch signal at a reference switch, connected to a reference voltage source, wherein the reference switch changes from an open state to a closed state, wherein the reference voltage source is electrically connected to an input of a servo amplifier, and sends a reference voltage to the servo amplifier.

In another embodiment, a linear isolation amplifier may include a servo amplifier, disposed on a high voltage side of the linear isolation amplifier, and an output amplifier, disposed on a low voltage side of the linear isolation amplifier. The linear isolation amplifier may include a first optocoupler circuit, electrically coupled to an output side of the servo amplifier, and comprising a first LED, optically coupled to an input side of the output amplifier, and a calibration circuit, electrically coupled to the output amplifier, to generate a calibration initiation signal. The linear isolation amplifier may further include a second optocoupler circuit, electrically coupled to the calibration circuit, and disposed to receive the calibration initiation signal, and further comprising a second LED, optically coupled to a reference switch on the high voltage side, wherein the reference switch is arranged to reversibly provide a reference voltage to the servo amplifier.

DESCRIPTION OF EMBODIMENTS

The present embodiments will now be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments are shown. The embodiments are not to be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey their scope to those skilled in the art. In the drawings, like numbers refer to like elements throughout.

In the following description and/or claims, the terms “on,” “overlying,” “disposed on” and “over” may be used in the following description and claims. “On,” “overlying,” “disposed on” and “over” may be used to indicate that two or more elements are in direct physical contact with one another. Also, the term “on,”, “overlying,” “disposed on,” and “over”, may mean that two or more elements are not in direct contact with one another. For example, “over” may mean that one element is above another element while not contacting one another and may have another element or elements in between the two elements. Furthermore, the term “and/or” may mean “and”, it may mean “or”, it may mean “exclusive-or”, it may mean “one”, it may mean “some, but not all”, it may mean “neither”, and/or it may mean “both”, although the scope of claimed subject matter is not limited in this respect.

In various embodiments, systems, devices, and techniques are provided for automatic calibration of an isolation amplifier, such as for unity in transfer gain. According to some embodiments, as described hereinbelow, circuitry is disclosed to provide illustration of functional equivalents for implementing self-calibration of an isolation amplifier, where the details of actual components, and circuit arrangements for implementing the calibration may vary, as will be understood by those of ordinary skill in the art.

Turning toFIG. 1Athere is shown an amplifier circuit100, according to various embodiments of the disclosure. The amplifier circuit100may function as a unipolar linear amplifier according to various embodiments. The amplifier circuit100is arranged as a linear isolation amplifier, having a high voltage side102and low voltage side104. For convenience of description, various portions of the amplifier circuit100may be grouped into various circuits that are linked together as shown, while other groupings are possible to describe the same amplifier circuit. As further shown inFIG. 1A, the amplifier circuit100includes an isolated amplifier circuit106, disposed on the high voltage side102of the amplifier circuit100, and arranged to generate an isolated output signal. The amplifier circuit100further includes a first optocoupler circuit108, disposed to receive the isolated output signal from the isolated amplifier circuit106, and an output amplifier circuit110, disposed on a low voltage side104of the amplifier circuit100, and coupled to receive an optical output signal from the first optocoupler circuit108.

The amplifier circuit100further includes a calibration circuit112, coupled to the output amplifier circuit110, to generate a calibration initiation signal, and a second optocoupler circuit,114, disposed to receive the calibration initiation signal, and to output a switch signal, so that a reference voltage is output to the isolated amplifier circuit106. As such, the amplifier circuit100may be arranged to automatically perform a calibration (or self-calibration), for example, at system startup, or upon demand, wherein the transfer gain may be calibrated to a fixed value, such as “1”.

In the embodiment specifically depicted inFIG. 1A, the isolated amplifier circuit106further includes a differential amplifier122, having a differential amplifier output node, as well as a servo amplifier124, having a servo output to generate the isolated output signal. This isolated output signal may cause the first optocoupler circuit108to generate an optical signal to be received by the low voltage side104, as described below.

The isolated amplifier circuit106may include a first switch126, which switch may act as a main switch, disposed between the differential amplifier output node and an input of the servo amplifier124, and a second switch128, coupled on a first side to the second optocoupler circuit114, and coupled on a second side to the input of the servo amplifier. The isolated amplifier circuit106may further include a first reference voltage source130, having an output coupled to the switch.

As depicted inFIG. 1A, the first optocoupler circuit108may be arranged similarly to known optocouplers, including a first light emitting diode (LED)132, coupled between a voltage source line (VCC1) and the servo amplifier124, a first photodetector134, disposed on the high voltage side102, coupled to receive an LED output from the first LED132, and further coupled to the input of the servo amplifier124. The first optocoupler circuit108may include a second photodetector136, disposed on the low voltage side104, coupled to receive the LED output from the first LED132, and further coupled to output amplifier circuit110.

As regards the output amplifier circuit110, this circuit may include an output amplifier140, having an input coupled to the second photodetector136, and a multiplying digital to analog converter (MDAC)142, coupled to the output amplifier140and to the calibration circuit112.

In operation, the amplifier circuit100may be arranged to perform a calibration procedure, such as at startup, or upon user demand, in accordance with embodiments of the disclosure. Advantageously, the amplifier circuit100may be arranged to automatically calibrate the transfer gain to a value of 1, as detailed in the description to follow. To facilitate calibration upon startup, the calibration circuit112may include a controller150, where the controller150may be arranged as a microcontroller to perform various known operations to control the amplifier circuit100. For calibration procedures, the controller150may be arranged to output a control signal, where the calibration circuit112further includes a calibration pin152to receive the control signal and to output a LOW signal to the second optocoupler circuit114, upon receipt of the control signal. For example, when the amplifier circuit100is powered on, the controller150may initiate a set of operations, including sending the control signal to the calibration pin152to hold the line low.

According to some embodiments, the second optocoupler circuit114may include a second LED154, acting as a calibration LED and coupled to receive the low signal from the calibration pin152, so as to output a second LED signal.FIG. 1Billustrates an implementation of a calibration portion of the isolated amplifier circuit ofFIG. 1A. As shown inFIG. 1B, the controller150may include a power on reset (POR) circuit151.FIG. 1Cillustrates the timing of signals of a calibration procedure according to embodiments of the disclosure, using the POR circuit151, for example. The Y-axis indicates voltage and X-axis indicates time. As shown inFIG. 1C, when power is applied on low side, between time T1and time T2, LED2C and MDAC input is held low, generating the low signal received by the second LED154, to cause current to flow through the second LED154. The low signal on LED2C continues until the MDAC indicates calibration is complete. At that time (T2) LED2C goes high, so the LED2C is turned off.

The second optocoupler circuit114may also include a third photodetector156, coupled to receive the second LED signal and to output the switch signal that is sent to the isolated amplifier circuit106.

In normal operation, the amplifier circuit100may work as an isolation amplifier where the amplifier circuit100is manufactured to generate a designed transfer gain, such as a value of 1 or 1.0, or 1.00, depending upon the degree of accuracy needed. Because of variations in properties of circuitry due to process variation used to form the various components, among other factors, the isolation amplifier100, without correction, may yield a transfer gain different from the targeted value. Accordingly, in some implementations, the controller150may be configured to automatically, or upon user input, perform a calibration operation to automatically adjust the transfer gain to the target value, such as 1.0.

In one specific implementation, the first switch126is set to a closed position and second switch128is set to an open position during a powered off state. At the same time, the MDAC is set a default resistance value. Upon power up, the controller150may generate a signal that is sent to the calibration pin152to hold the calibration pin low, meaning the voltage on the line (LED2C) between the calibration pin152and the cathode of a calibration LED, meaning the second LED154, is held low. At the same time, the anode of the second LED154is coupled to a VCC2 voltage source (disposed on the low voltage side104) via line LED2A, where the voltage difference may cause the second LED154to generate a second LED signal that may be received by a detector, such as the third photodetector156, disposed on the high voltage side102. The controller150may be programmed to set the calibration pin152in a low state for a predetermined interval, so that the cathode voltage on the second LED154remains low and current flows through the second LED. When current flows through the P/N junction of the second LED154, a light signal is generated by the second LED154during the predetermined interval.

As a consequence, the light signal generated by the second LED154is received by the third photodetector156, on the high voltage side102, for the predetermined interval. In different implementations, the third photodetector156may be arranged as a photodiode or a transistor, as shown in more detail inFIG. 2. The third photodetector156, coupled to the first switch126and the second switch128, may then generate a signal to change the first switch126from a closed to an open state, and to change the second switch128(reference switch) from an open state to a closed state.

As further illustrated inFIG. 1A, when the second switch128is in a closed state, the first reference voltage source130is electrically connected to the input of the servo amplifier124via the resistor R1. In one embodiment, for example, the first reference voltage source130may generate a voltage of 1.2 V that is applied through the resistor R1.

Notably, after the reference voltage is applied to the input of servo amplifier124, in turn the servo amplifier124is arranged to output a signal, a voltage to the cathode of the first LED132, disposed on the high voltage side102. In turn, based upon the voltage of VCC1, coupled to the anode of the first LED132, current will flow through the first LED132, wherein a calibration light signal is generated, to be detected, for example, by the first photodetector134, disposed on the high voltage side102, as well as by the second photodetector136, disposed on the low voltage side104.

As further shown inFIG. 1A, the MDAC142is coupled to the calibration pin152, and may therefore detect that the amplifier circuit100is in calibration mode during the predetermined interval, where the first switch126is open and second switch128is closed. Knowing that the reference voltage (e.g., 1.2 V) is being applied to the servo amplifier124and that a calibration mode is presently active, the MDAC142may adjust the output of the output amplifier140to match the voltage on the high voltage side102, that is, to the reference voltage value form the first reference voltage source130, such as 1.2 V. Accordingly, a transfer gain value of 1 (=1.2V/1.2V) will be established.

Returning toFIG. 1A, after the predetermined interval elapses, the controller150may send a second signal to bring the calibration pin152high (to a high state), turning off the second LED154. Once the second LED154is turned off, the third photodetector156no longer receives a light signal, and the first switch126returns to a closed position, while the second switch128returns to an open position. The amplifier circuit100has now been calibrated to generate a transfer gain of 1, for example, as is ready for use.

In other embodiments of the disclosure, an analog to digital (ADC) converter may be added to the isolation amplifier circuitry as disclosed above. Turning toFIG. 2, there is shown an amplifier circuit200, in accordance with further embodiments of the disclosure. In this embodiment, a circuit202on the low voltage side104is provided, including ADC204, coupled to the MDAC142and the output amplifier140. An integrated ADC allows the user to digitally resolve the value. This configuration, off-loads the user work to give a simple digital interface.

Turning now toFIG. 3, there is shown one circuit arrangement for performing autogain setting in an MDAC according to some embodiments of the disclosure. In this example, an MDAC arrangement160is shown, and may include a comparator162, having a first input that receives a reference voltage, shown as VREF 1.200 V inFIG. 3. The comparator162includes a second input to receive an inverting input signal, which signal is generated at the output of the output amplifier140, as shown inFIG. 3. The output of the comparator162is coupled to a counter164(an up/down counter), thus coupled to receive an output signal from the comparator162. The counter164may be arranged to count up when the output signal from comparator162high, for example.

The MDAC arrangement160may further include a first FET assembly166and a second FET assembly168, coupled to the counter164. Each of first FET assembly166and second FET assembly168may include one or more field effect transistors, coupled to a given resistor (shown as R45 and R46), depending upon the desired resolution of transfer gain to be set. In other words, for an embodiment of an 8-bit counter, 8 field effect transistors in the MDAC arrangement160. More generally, an n-bit counter will be provided with n field effect transistors.

In addition, the MDAC arrangement160also includes a clock170, where the clock170is arranged to receive the calibration initiation signal (CAL) from the calibration pin152, and to send a clock signal to the counter164.

Assuming the case where transfer gain is to be set at 1 for an amplifier circuit, such as amplifier circuit100, and assuming the reference voltage on the high voltage side is set at 1.2 V, then the output on the low voltage side, containing the MDAC arrangement160, is also to be set at 1.2 V. Referring toFIG. 3, where the VREF 1.200 V is received at the first input of the comparator162(U23), the MDAC arrangement160may operate as follows. If the inverting input (inverting voltage) received from output amplifier140is below the VREF (meaning below 1.2 V is this particular example), the output of the comparator will go high (output a high signal) and the counter will count up. If the inverting input received from the output amplifier140, on the other hand, is above VREF (i.e., >1.2 V), the comparator162will go low, and this low output will cause the counter164to count down. As noted, inFIG. 3, M1 and M2 represent N-number of FETs depending on desired gain resolution. As the counter164counts up, the FETs are turned off until the gain is set such that the output of output amplifier140is equal to 1.200V. In particular, the counter164may then count in a binary fashion turning on and off the different field effect transistors until the combined parallel resistances generate an output of the output amplifier140that matches the reference voltage to comparator162. At some point, such as after a predetermined interval, the controller150will send a signal to the calibration pin152so that the calibration initiation signal is de-asserted and the clock170turns off. When the clock170turns off, the counter164is arranged to stay frozen in the last state (the current count state) representing the trimmed count at the instance the clock170is turned off.

Also, in accordance with embodiments of the disclosure, as calibration mode is exited, the amplifier, such as amplifier circuit100may self-configure as a standard LOC linear amplifier, except the trimming procedure performed according toFIG. 3, has set the transfer gain K3=1.

FIG. 4AandFIG. 4Bdepict another amplifier circuit, shown as amplifier circuit400, according to further embodiments of the disclosure. In this embodiment, the same semiconductor die, shown as die402and die404may be used on both a high voltage side102B and a low voltage side104B of the amplifier circuit400. This arrangement may employ bond out options to achieve the isolation amplifier function. The function pins are described in Table I when using on left side and right side of barrier. While not all the functions are used on each die of die402and die404in this “symmetric die” configuration, using the same dice has substantial advantages for manufacturing of an isolation amplifier, including allowing economies of scale. This approach allows one type of semiconductor wafer for fabricating the amplifier product instead of two different types of semiconductor wafer. This approach also provides the benefit where die to die variation is very small, since the die for the same amplifier may be manufactured on the same wafer.

FIG. 5depicts a process flow500, according to embodiments of the disclosure. At block502, a linear isolation amplifier is switched from an OFF state to an ON state. The switching on may trigger a microcontroller or other device to send a calibration initiation signal for a predetermined interval during the ON state. For example, the microcontroller may reside on a low voltage side of the linear isolation amplifier, and may send a signal to trigger a calibration pin to a low state.

At block504, a signal is sent from a low voltage side to the high voltage side of the linear isolation amplifier to provide a first reference voltage to a servo amplifier. For example, the first reference voltage may represent a calibration voltage. In some implementations, the signal may be sent through an optocoupler between the low voltage side and high voltage side, causing a switch to couple a reference voltage source to the servo amplifier.

At block506a first photocurrent and second photocurrent are generated in a first main photodetector, disposed on the high voltage side, and a second main photodetector, disposed on the low voltage side, respectively. This photocurrent may be automatically generated by an optocoupler when the servo amplifier receives the first reference voltage.

At block508, the second photocurrent is received at a first input of an output amplifier, disposed on the low voltage side. At block510, the output amplifier generates an output voltage. At block512, the output voltage is received at a first input of a comparator.

At decision block514the output voltage is compared to a second reference voltage received at a second input of the comparator. The second reference voltage may be set to be equal to the first reference voltage on the high voltage side. If the output voltage is the same as the second reference voltage, the flow proceeds to block516, where the calibration mode ends.

If, at decision block514, the output voltage is greater than the second reference voltage, the flow proceeds to block518, where a counter, coupled to the output amplifier, is counted down. This counting down accordingly adjusts the input voltage to the output amplifier. The flow then returns to block512.

If, at decision block514, the output voltage is less than the second reference voltage, the flow proceeds to block520, where a counter, coupled to the output amplifier, is counted up. This counting up accordingly adjusts the input voltage to the output amplifier. The flow then returns to block512.

While the present embodiments have been disclosed with reference to certain embodiments, numerous modifications, alterations and changes to the described embodiments are possible while not departing from the sphere and scope of the present disclosure, as defined in the appended claims. Accordingly, the present embodiments are not to be limited to the described embodiments, and may have the full scope defined by the language of the following claims, and equivalents thereof.