US-12620952-B2 - Drive circuit for inductive position transducer system

Abstract

An inductive position transducer system includes a drive circuit and an inductive position transducer with at least a first field generating coil. The drive circuit includes a resonant circuit portion and an amplifier portion. The amplifier portion comprises a current-driven single stage differential amplifier and is configured to provide an oscillating drive signal to the resonant circuit portion which results in a driving of the field generating coil (e.g., at a coil voltage which may be larger than a power supply voltage, such as over 2× larger). A controller may adjust a bias current that is provided to the amplifier portion to maintain the voltage across the field generating coil (e.g., at a specified voltage level). The amplifier portion may comprise CMOS transistors and may be fabricated on a chip (as part of a low-voltage CMOS integrated circuit) along with other portions of the inductive position transducer system.

Inventors

• Patrick H. Mawet

Assignees

• MITUTOYO CORPORATION

Dates

Publication Date

20260505

Application Date

20221228

Claims (20)

1. 1 . An inductive position transducer system, comprising: an inductive position transducer comprising at least a first field generating coil having a first coil terminal, a second coil terminal and a coil impedance; a drive circuit configured to drive the first field generating coil, the drive circuit comprising: a resonant circuit portion connected to the first and second coil terminals, the resonant circuit portion comprising at least a first resonant circuit portion component, a second resonant circuit portion component, and a third resonant circuit portion component, wherein the first resonant circuit portion component is coupled between a first resonant circuit portion node and a second resonant circuit portion node, the first resonant circuit portion node is separated from the first coil terminal by at least the second resonant circuit portion component, and the second resonant circuit portion node is separated from the second coil terminal by at least the third resonant circuit portion component; and an amplifier portion connected to the first and second resonant circuit portion circuit nodes, the amplifier portion having an output impedance during operation, wherein the amplifier portion is configured to provide an oscillating drive signal at the first and second resonant circuit portion nodes, the amplifier portion comprising a current-driven single stage differential amplifier, the current-driven single stage differential amplifier comprising first and second amplifier inputs and first and second amplifier outputs, with the first amplifier output connected to the first resonant circuit portion node and the second amplifier output connected to the second resonant circuit portion node; and a controller, wherein the amplifier portion comprises a bias current portion that receives a bias current from the controller, for which the controller is configured to provide the bias current to the amplifier portion to keep a voltage across the first field generating coil at a specified voltage level; wherein a resonator portion comprising at least the resonant circuit portion and the first field generating coil has a resonant frequency and a load impedance presented to the amplifier portion during operation.
2. 2 . The inductive position transducer system of claim 1 , wherein the current driven single stage differential amplifier comprises a first single stage amplifier portion and a second single stage amplifier portion.
3. 3 . The inductive position transducer system of claim 2 , wherein the first and second single stage amplifier portions comprise metal-oxide-semiconductor transistors.
4. 4 . The inductive position transducer system of claim 2 , wherein the first and second single stage amplifier portions are each complimentary amplifier portions which each comprise a p-channel MOS transistor and an n-channel MOS transistor.
5. 5 . The inductive position transducer system of claim 2 , wherein: the first single stage amplifier portion comprises a first n-channel MOS transistor and a first p-channel MOS transistor, with the gates of the first NMOS and PMOS transistors coupled together to provide the first amplifier input and the drains of the first NMOS and PMOS transistors coupled together to provide the second amplifier output; and the second single stage amplifier portion comprises a second NMOS transistor and a second PMOS transistor, with the gates of the second NMOS and PMOS transistors coupled together to provide the second amplifier input and the drains of the second NMOS and PMOS transistors coupled together to provide the first amplifier output.
6. 6 . The inductive position transducer system of claim 1 , wherein the bias current portion comprises two MOS transistors which form a current mirror.
7. 7 . The inductive position transducer system of claim 1 , wherein the controller is configured to adjust the bias current that is provided to the amplifier portion to maintain the voltage across the first field generating coil at a specified voltage level, such that: at a first time, the controller is configured to provide the bias current at a first bias current level which results in a voltage across the field generating coil that is at the specified voltage level; and at a second time, the controller providing the bias current at the first bias current level results in a voltage across the field generating coil that is not at the specified voltage level, for which the controller is configured to adjust the bias current from the first bias current level to a second bias current level which results in a voltage across the field generating coil that is at the specified voltage level.
8. 8 . The inductive position transducer system of claim 1 , wherein the controller is configured to: provide the bias current to the amplifier portion to keep the voltage across the first field generating coil at the specified voltage level during a first state when the inductive position transducer system is performing measurement operations; and not provide the bias current to the amplifier portion to keep the voltage across the first field generating coil at the specified voltage level during a second state when the inductive position transducer system is not performing measurement operations.
9. 9 . The inductive position transducer system of claim 1 , comprising a semiconductor chip on which both the amplifier portion and the resonant circuit portion are included as part of an integrated circuit.
10. 10 . The inductive position transducer system of claim 9 , wherein the current-driven single stage differential amplifier of the amplifier portion comprises metal oxide semiconductor transistors.
11. 11 . The inductive position transducer system of claim 1 , wherein the amplifier portion receives and operates based on a power supply voltage.
12. 12 . The inductive position transducer system of claim 11 , further comprising a demodulator portion, wherein the demodulator portion receives and operates based on the same power supply voltage as the amplifier portion.
13. 13 . The inductive position transducer system of claim 11 , wherein an impedance transformer portion comprises the resonant circuit portion, and through utilization of the current-driven single stage differential amplifier and the impedance transformer portion the drive circuit is configured to produce a voltage across the field generating coil that is larger than the power supply voltage.
14. 14 . The inductive position transducer system of claim 1 , wherein the drive circuit further comprises: a first filter portion connected to the first coil terminal and the first amplifier input of the current-driven single stage differential amplifier; and a second filter portion connected to the second coil terminal and the second amplifier input of the current-driven single stage differential amplifier.
15. 15 . The inductive position transducer system of claim 14 , wherein: the first filter portion comprises a first filter portion capacitor and a first filter portion resistor which are coupled in series between the first coil terminal and the first amplifier input; and the second filter portion comprises a second filter portion capacitor and a second filter portion resistor which are coupled in series between the second coil terminal and the second amplifier input.
16. 16 . The inductive position transducer system of claim 14 , wherein: the first filter portion comprises a respective first filter portion first node connected to the first coil terminal, and a first filter portion second node, and the second filter portion comprises a second filter portion first node connected to the second coil terminal, and a second filter portion second node; the first amplifier output of the differential amplifier is connected to the first resonant circuit portion node and to a first terminal of a first bias resistor; the second amplifier input of the differential amplifier is connected to a second terminal of the first bias resistor; the first amplifier input of the differential amplifier is connected to the respective first filter portion second node; the second amplifier output of the differential amplifier is connected to the second resonant circuit portion node and to a first terminal of a second bias resistor; the first amplifier input of the differential amplifier is connected to a second terminal of the second bias resistor; and the second amplifier input of the differential amplifier is connected to the respective second filter portion second node.
17. 17 . The inductive position transducer system of claim 16 , wherein: the first filter portion comprises at least one first filter portion capacitor having a respective first terminal connected to the first coil terminal, and a respective second terminal connected to a first terminal of at least one respective first filter portion resistor; and the second filter portion comprises at least one respective second filter portion capacitor having a respective first terminal connected to the second coil terminal, and a respective second terminal connected to a first terminal of at least one respective second filter portion resistor.
18. 18 . The inductive position transducer system of claim 17 , wherein: a second terminal of the at least one respective first filter portion resistor is connected to the first amplifier input; and a second terminal of the at least one respective second filter portion resistor is connected to the second amplifier input.
19. 19 . The inductive position transducer system of claim 18 , wherein: the first resonant circuit portion component comprises a first resonant circuit capacitor which is connected between the first and second resonant circuit portion nodes; and the second resonant circuit portion component comprises a second resonant circuit capacitor which has a respective first terminal connected to the first resonant circuit portion node, and a respective second terminal connected to the first coil terminal; and the third resonant circuit portion component comprises a third resonant circuit capacitor which has a respective first terminal connected to the second resonant circuit portion node, and a respective second terminal connected to the second coil terminal.
20. 20 . A method of operating an inductive position transducer system which includes an inductive position transducer comprising at least a first field generating coil having a first coil terminal, a second coil terminal and a coil impedance, the method comprising: operating a drive circuit of the inductive position transducer system to drive the first field generating coil, the drive circuit comprising: a resonant circuit portion connected to the first and second coil terminals, the resonant circuit portion comprising at least a first resonant circuit portion component, a second resonant circuit portion component, and a third resonant circuit portion component, wherein the first resonant circuit portion component is coupled between a first resonant circuit portion node and a second resonant circuit portion node, the first resonant circuit portion node is separated from the first coil terminal by at least the second resonant circuit portion component, and the second resonant circuit portion node is separated from the second coil terminal by at least the third resonant circuit portion component; and an amplifier portion connected to the first and second resonant circuit portion circuit nodes, the amplifier portion having an output impedance during operation, wherein the amplifier portion is configured to provide an oscillating drive signal at the first and second resonant circuit portion nodes, the amplifier portion comprising a current-driven single stage differential amplifier, the current-driven single stage differential amplifier comprising first and second amplifier inputs and first and second amplifier outputs, with the first amplifier output connected to the first resonant circuit portion node and the second amplifier output connected to the second resonant circuit portion node; wherein a resonator portion comprising at least the resonant circuit portion and the first field generating coil has a resonant frequency and a load impedance presented to the amplifier portion during operation; adjusting a bias current of the current-driven single stage differential amplifier to correspondingly adjust a voltage across the first field generating coil; and providing an output based at least in part on a position-dependent signal from the inductive position transducer.

Description

BACKGROUND Technical Field This disclosure relates to metrology and, more particularly, to inductive position transducer systems. Description of the Related Art Inductive position transducers are widely used to measure relative displacements between one or more sensing elements (e.g., which may alternatively be referred to as receiver winding elements) and one or more disrupting elements (e.g., scale elements) that modulate the inductive coupling between the sensing elements and a field generating coil (e.g., which may alternatively be referred to as a transmitter winding). In various conventional inductive position transducers (e.g., such as those disclosed in U.S. Pat. Nos. 6,005,387 and 6,011,389, each of which is hereby incorporated herein by reference in its entirety), a lower power, intermittent drive circuit is used to supply a time-varying drive signal to the field generating coils. In the '389 and '387 patents, the intermittent drive circuit discharges a capacitor through the inductor formed by the field generating coil. This causes the field generating coil to “ring”. That is, the current released by connecting the charged capacitor to ground through the inductor formed by the field generating coil and a serially-connected resistor oscillates and exponentially decays. While the field generating coil drive circuits disclosed in the '389 and '387 patents are suitable for inductive position transducers designed for certain operations, they may have certain limitations (e.g., in relation to speed, resolution, etc.). In addition, for various previously known inductive position transducers, when an inductance of a drive coil does not participate in determining the oscillation frequency of the conventional drive circuits, the transducer signal output is detrimentally reduced to the extent that the oscillation frequency of the field generating coil does not coincide with the resonant frequency of the field generating coil. A drive circuit with improved characteristics would be desirable. BRIEF SUMMARY This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This summary is not intended to identify key features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter. An inductive position transducer system is provided which includes an inductive position transducer and a drive circuit. The inductive position transducer comprises at least a first field generating coil. The drive circuit is configured to drive the first field generating coil. The first field generating coil has a first coil terminal, a second coil terminal and a coil impedance. The drive circuit includes a resonant circuit portion and an amplifier portion. The resonant circuit portion is connected to the first and second coil terminals. The resonant circuit portion comprises at least a first resonant circuit portion component, a second resonant circuit portion component, and a third resonant circuit portion component (e.g., wherein each resonant circuit portion component comprises a respective capacitor). The first resonant circuit portion component is coupled between a first resonant circuit portion node and a second resonant circuit portion node, the first resonant circuit portion node is separated from the first coil terminal by at least the second resonant circuit portion component, and the second resonant circuit portion node is separated from the second coil terminal by at least the third resonant circuit portion component. The amplifier portion is connected to the first and second resonant circuit portion circuit nodes, the amplifier portion having an output impedance during operation. The amplifier portion is configured to provide an oscillating drive signal at the first and second resonant circuit portion nodes. The amplifier portion comprises a current-driven single stage differential amplifier. The differential amplifier comprises first and second amplifier inputs and first and second amplifier outputs, with the first amplifier output connected to the first resonant circuit portion node and the second amplifier output connected to the second resonant circuit portion node. A resonator portion comprising at least the resonant circuit portion and the first field generating coil has a resonant frequency and a load impedance presented to the amplifier portion during operation. In various implementations, a controller is configured to adjust a bias current that is provided to the amplifier portion to maintain the voltage across the first field generating coil at a specified voltage level. In various implementations, the amplifier portion includes MOS transistors and may be fabricated on a chip (e.g., along with other portions of the inductive position transducer system). In various implementations, a method is provided for operating the inductive position transducer system. The met