Search

CN-122029737-A - Bias circuit for crystal oscillator

CN122029737ACN 122029737 ACN122029737 ACN 122029737ACN-122029737-A

Abstract

A bias circuit may generate one or more bias outputs for a crystal oscillator. The bias circuit may include a first current mirror, a second current mirror, and a third current mirror. The capacitor may be coupled between the second current mirror and the third current mirror. In operation, the first bias output may be generated by the third current mirror and the second bias output may be generated by the second current mirror. The first bias output and the second bias output may be coupled to a crystal oscillator.

Inventors

  • J. Kotovski

Assignees

  • 微芯片技术股份有限公司

Dates

Publication Date
20260512
Application Date
20240419
Priority Date
20240103

Claims (16)

  1. 1. A bias circuit, the bias circuit comprising: A first current mirror comprising a current source coupled to a first current mirror device, the current source coupled to a first node and a second node of the first current mirror device, wherein a third node of the first current mirror device is coupled to a first fixed voltage; a second current mirror comprising a second current mirror device and a first cascode device, wherein: The first node and the second node of the first cascode device are coupled together and form a current path; the first node of the second current mirror device is coupled to a third node of the first cascode device; a second node of the second current mirror device is coupled to the current source; A third node of the second current mirror device is coupled to the first fixed voltage; a third current mirror comprising a third current mirror device and a second cascode device, wherein: a first node of the second cascode device is coupled to an output driver; a second node of the second cascode device is coupled to the second node of the first cascode device; a third node of the second cascode device is coupled to the first node of the third current mirror device; a second node of the third current mirror device is coupled to the current source; a third node of the third current mirror device is coupled to the first fixed voltage; Wherein the output driver includes a first node coupled to the first node of the second cascode device, a second node coupled to a first node of a capacitor, and a third node coupled to a second fixed voltage, the first node of the output driver includes a first bias output and the second node of the output driver includes a second bias output, and Wherein the capacitor includes a first node coupled to a second node of the output driver, and a second node coupled to the second node of the second cascode device.
  2. 2. The bias circuit of claim 1, the first fixed voltage comprising a positive supply voltage.
  3. 3. The bias circuit of any one of claims 1-2, the second fixed voltage comprising a negative supply voltage.
  4. 4. The bias circuit of any one of claims 1-2, the second fixed voltage comprising a ground loop.
  5. 5. The bias circuit of any one of claims 1-2, the second fixed voltage comprising a positive supply voltage.
  6. 6. The bias circuit of any one of claims 1-5, a current flowing through the current source being equal to twice a current flowing through the second current mirror device and the first cascode device.
  7. 7. The bias circuit of any one of claims 1 to 6, the third current mirror device having a size that is several times the size of the second current mirror device.
  8. 8. The bias circuit of any of claims 1-7, the second cascode device having a size that is several times the size of the first cascode device.
  9. 9. A crystal oscillator system, the crystal oscillator system comprising: A bias circuit for generating a first bias output and a second bias output based on a first current mirror, the first current mirror including a current source and a first current mirror device, and A crystal oscillator for receiving inputs from the first bias output and the second bias output and generating an oscillating output.
  10. 10. The crystal oscillator system of claim 9, the bias circuit comprising a second current mirror for receiving an input from the current source and a third current mirror for receiving an input from the current source.
  11. 11. The crystal oscillator system of claim 10, the second current mirror comprising a second current mirror device coupled to a first cascode device.
  12. 12. The crystal oscillator system of any one of claims 10 to 11, the third current mirror comprising a third current mirror device coupled to a second cascode device, and an output driver coupled to the second cascode device.
  13. 13. The crystal oscillator system of any one of claims 9 to 12, comprising a capacitor coupled between the output driver and the second cascode device.
  14. 14. A method, the method comprising: generating a reference current in a first current mirror; generating a first bias output, the first bias output based on the reference current; Generating a second bias output, the second bias output being based on the reference current, and The first bias output and the second bias output are output to a crystal oscillator.
  15. 15. The method of claim 14, generating a first bias output comprising generating a current in a second current mirror that is half of a value of the reference current.
  16. 16. The method of any of claims 14 to 15, generating a first bias output comprising generating a current in a third current mirror, the current in the third current mirror being a multiple of the current in the second current mirror.

Description

Bias circuit for crystal oscillator Priority This patent application claims priority from commonly owned U.S. provisional patent application 63/544,795 filed on day 2023, 10, 19, the entire contents of which are hereby incorporated by reference for all purposes. Technical Field The present disclosure relates to a bias circuit for a crystal oscillator. Background The crystal oscillator may be driven with an input from an AC coupled driver circuit. Such examples may include high value resistors when using current levels below 100 nA. As one of various examples, the resistor value may exceed 1mΩ. Crystal oscillators employing high-value resistors can be bulky and expensive. Other examples may utilize class a or class C amplifiers, which may represent a less efficient solution, possibly resulting in wasted current. There is a need for a bias circuit that can operate at low current bias points without the use of high value resistors and that provides a bias current for the crystal oscillator. Disclosure of Invention Examples herein implement a device for generating a bias current for a crystal oscillator. According to one aspect, a bias circuit includes a first current mirror including a current source coupled to a first current mirror device. The current source may be coupled to a first node and a second node of the first current mirror device. The third node of the first current mirror device may be coupled to a first fixed voltage. The second current mirror may include a second current mirror device and a first cascode device. The first node and the second node of the first cascode device may be coupled together and form a current path. The first node of the second current mirror device may be coupled to a third node of the first cascode device. The second node of the second current mirror device may be coupled to a current source. The third node of the second current mirror device may be coupled to a first fixed voltage. The third current mirror may include a third current mirror device and a second cascode device. The first node of the second cascode device may be coupled to an output driver. The second node of the second cascode device may be coupled to the second node of the first cascode device. The third node of the second cascode device may be coupled to the first node of the third current mirror device. The second node of the third current mirror device may be coupled to a current source. The third node of the third current mirror device may be coupled to a first fixed voltage. The output driver includes a first node coupled to the first node of the second cascode device, a second node coupled to the first node of the capacitor, and a third node coupled to a second fixed voltage. The first node of the output driver may be a first bias output and the second node of the output driver may be a second bias output. The capacitor includes a first node coupled to the second node of the output driver, and a second node coupled to the second node of the second cascode device. According to one aspect, a system includes a bias circuit to generate a first bias output and a second bias output based on a first current mirror. The first current mirror may include a current source and a first current mirror device. The system may include a crystal oscillator to receive inputs from the first bias output and the second bias output and to generate an oscillating output. According to one aspect, a method includes generating a reference current in a first current mirror, generating a first bias output, the first bias output based on the reference current, generating a second bias output, the second bias output based on the reference current, and outputting the first bias output and the second bias output to a crystal oscillator. Drawings Fig. 1 illustrates one of various examples of bias circuits. Fig. 2 illustrates one of various examples of a crystal oscillator system. Fig. 3 illustrates a timing diagram of a bias circuit and a crystal oscillator system. Fig. 4 illustrates a method of biasing a crystal oscillator. Detailed Description Fig. 1 illustrates one of various examples of a bias circuit 100 for a crystal oscillator. The bias circuit 100 may include a current source 110. The current source 110 may be a controlled current source or an independent current source. The current source 110 may be a current mirror or may be another type of current source not specifically mentioned. The current source 110 may generate a reference current. The current source 110 may be coupled to a first current mirror device 111. In one of various examples, the current source 110 may be coupled to a first node and a second node of the first current mirror device 111. In one of various examples, the first current mirror device 111 may include a Metal Oxide Semiconductor Field Effect (MOSFET) device, and the current source 110 may be coupled to a drain node and a gate node of the first current mirror device 111. The third node of the first