A subharmonic injection locked oscillator for a medical implant communication system
Patent Information
- Application Number
- CN202611135380.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-07-29
- Publication Date
- 2026-10-20
AI Technical Summary
收发机传统的频率合成技术通常是锁相环（PLL），它不仅功耗和面积大，低电源电压下也不易稳定工作，而且启动时间慢，无法使用激进的占空比来最小化静态功耗
[0014]本发明的有益效果为：本发明的亚谐波注入锁定振荡器采用高集成度的架构，可满足医疗植入通信系统的低电压、低功耗、低芯片面积的要求。本发明通过亚谐波注入锁定技术，可实现低功耗倍频，并显著抑制环形振荡器的相位噪声；采用尾电流源预失真线性化技术，在低电源电压下实现了收发机本振频率的线性调谐。同时环形振荡器的启动时间比锁相环短，可使用激进的占空比来最小化静态功耗。通过这些技术，使得该设计可满足医疗植入通信系统的要求。
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Abstract
Description
Technical Field
[0001] This invention belongs to the field of integrated circuit technology, and specifically relates to a subharmonic injection-locked oscillator for medical implant communication systems. Background Technology
[0002] Power consumption is one of the most critical requirements for medical implantable communication systems. Future biosensor systems-on-a-chip (SoCs) may contain a wide variety of circuit components, including electrophysiological sensor interfaces, analog-to-digital converters (ADCs), digital signal processors (DSPs), microprocessors, power management units (Power Management Units), and wireless transceivers. Among these components, the wireless transceiver is typically the primary power consumer. Operating the transceiver near its threshold region can improve power consumption per bit. However, as the supply voltage approaches this threshold region, issues such as limited voltage margin, component variations, and leakage become significant.
[0003] Meanwhile, for size-constrained medical applications, reducing the number of external components and chip area is a crucial factor, prompting the adoption of simplified, highly integrated architectures. Traditional transceiver frequency synthesis techniques typically utilize phase-locked loops (PLLs), which are not only power-hungry and area-intensive, but also difficult to operate stably at low supply voltages, have slow startup times, and cannot utilize aggressive duty cycles to minimize static power consumption. Free-running ring oscillators can achieve reduced power consumption and area, but their phase noise and spurious degradation generally do not meet the requirements of communication-based medical implant systems. Summary of the Invention
[0004] To address the shortcomings of existing technologies, this invention proposes a subharmonic injection-locked oscillator for a medical implantable communication system, comprising: a single-ended injection inverter, an AC coupling capacitor, a ring oscillator, and a tail current source; the output terminal of the single-ended injection inverter is connected to one end of the AC coupling capacitor, and the other end of the AC coupling capacitor is connected to the ring oscillator; the ring oscillator is connected to the tail current source.
[0005] Preferably, the ring oscillator includes five single-ended inverters connected in series, with the output of the last single-ended inverter connected to the input of the first single-ended inverter; the sources of the five single-ended inverters are all connected to the output of the tail current source.
[0006] Preferably, the tail current source is a 32-bit thermometer-coded current source, which is composed of 32 tail transistors connected in parallel in sequence, and each tail transistor has a switch at its gate and is connected to a bias voltage; the drains of the 32 tail transistors are connected and serve as the output terminals of the tail current source and are connected to a ring oscillator; the sources of the 32 tail transistors are all grounded.
[0007] Furthermore, the drain-source voltage of the tail transistor in the tail current source is less than 50mV.
[0008] Furthermore, the dimensions of the tail transistor in the tail current source must meet the following requirements:
[0009]
[0010]
[0011] in, This indicates the width-to-length ratio of the 0th tail transistor of the tail current source. This represents the width-to-length ratio of the nth tail transistor of the tail current source, where n is an integer from 0 to 31; This indicates the channel width of the tail transistor. This indicates the channel length of the tail transistor.
[0012] Preferably, when the subharmonic injection locked oscillator is in use, a subharmonic signal is injected into the input terminal of its injection inverter.
[0013] Preferably, the free oscillation frequency of the ring oscillator is The injection frequency of the subharmonic signal is ; It is the frequency of the injected subharmonic signal, N is Integers.
[0014] The beneficial effects of this invention are as follows: The subharmonic injection-locked oscillator of this invention adopts a highly integrated architecture, which can meet the requirements of low voltage, low power consumption, and low chip area for medical implantable communication systems. This invention achieves low-power frequency doubling and significantly suppresses the phase noise of the ring oscillator through subharmonic injection-locked technology; it also achieves linear tuning of the transceiver local oscillator frequency under low supply voltage by employing tail current source predistortion linearization technology. Simultaneously, the ring oscillator has a shorter startup time than a phase-locked loop, allowing for the use of an aggressive duty cycle to minimize static power consumption. These technologies enable this design to meet the requirements of medical implantable communication systems. Attached Figure Description
[0015] Figure 1 This is a structural diagram of the subharmonic injection locked oscillator in this invention. Detailed Implementation
[0016] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0017] This invention proposes a subharmonic injection-locked oscillator for medical implant communication systems, such as... Figure 1As shown, the subharmonic injection-locked oscillator includes: a single-ended injection inverter, an AC coupling capacitor, a ring oscillator, and a tail current source; the output terminal of the single-ended injection inverter is connected to one end of the AC coupling capacitor, and the other end of the AC coupling capacitor is connected to the ring oscillator; the ring oscillator is connected to the tail current source.
[0018] In some preferred embodiments of the present invention, the ring oscillator is a single-ended, current-starved ring oscillator comprising five single-ended inverters connected in series, wherein the output of the last single-ended inverter is connected to the input of the first single-ended inverter; the sources of the five single-ended inverters are all connected to the output of the tail current source.
[0019] When the subharmonic injection lock-in oscillator is in use, a subharmonic signal is injected into the input terminal of its single-ended injection inverter; the free oscillation frequency of the ring oscillator is... The injection frequency of the subharmonic signal is ; Indicates the frequency of the injected subharmonic signal. for An integer. This means that the injection occurs once every N cycles. For example, you can choose... If the free oscillation frequency of the ring oscillator is Then the frequency of the injected subharmonic signal At this point, the system can achieve injection lock. In some applications, the injected subharmonic signal can be generated by a pulse generator. Such a structure can not only achieve frequency multiplication but also generate multiple time-interleaved phases A1-A5. In some applications, these five equally spaced phases can be passed through an edge combiner to generate a frequency five times higher.
[0020] In some preferred embodiments of the present invention, the tail current source is a 32-bit thermometer-coded current source, which is composed of 32 tail transistors connected in parallel in sequence. The tail transistors are NMOS transistors. Each tail transistor has a switch at its gate. The drains of the 32 tail transistors are connected and serve as the output terminals of the tail current source, which are connected to a ring oscillator. The sources of the 32 tail transistors are all grounded. In use, the gate of each tail transistor is connected to a bias voltage through a switch.
[0021] Because they operate near the threshold region, the drain-source voltage of the tail transistors in the tail current sources is extremely small, preferably less than 50mV. Therefore, these tail current source transistors operate in the linear region, rather than the desired saturation region. Consequently, these current source transistors are treated as resistors rather than current mirrors, and the time constant of the ring oscillator is dominated by the resistance of these tail transistors, rather than by the delay cells.
[0022] To linearize the tuning range of the oscillation frequency, the total parallel resistance of the turned-on tail transistors should decrease linearly with increasing thermometer value. Therefore, the dimensions of these current source transistors are pre-distorted to a specific set of values:
[0023]
[0024]
[0025] in, This indicates the aspect ratio of the 0th tail transistor M0 of the tail current source. M represents the nth tail transistor of the tail current source. n The aspect ratio, where n is an integer from 0 to 31. This indicates the channel width of the tail transistor. This indicates the channel length of the tail transistor.
[0026] Therefore, the total parallel resistance of the turned-on tail transistor is... for:
[0027]
[0028] in, This indicates that transistors M0, M1, ... M are turned on. , These are integers from 0 to 31. When operating under low supply voltage conditions, these resistor-like transistors can achieve a linear frequency tuning range.
[0029] In summary, the subharmonic injection-locked oscillator for medical implantable communication systems proposed in this invention uses a subharmonic injection-locking method for frequency synthesis near the threshold region. Simultaneously, it employs tail current source pre-distortion linearization technology to achieve linear tuning of the transceiver local oscillator frequency under low power supply voltage. When injection-locked, the injection-locked oscillator exhibits the same noise transfer function as a first-order phase-locked loop (PLL): the low-frequency portion tracks the low-frequency phase noise from the injected signal, and the high-frequency portion tracks the high-frequency phase noise during free oscillation of the oscillator. The frequency locking range... Similar to the bandwidth of a phase-locked loop (PLL). When the injection frequency... Equal to the free oscillation frequency of the oscillator The second harmonic time ( Subharmonic injection occurs, at which point the in-band phase noise is suppressed to... , This represents the low-frequency phase noise of the injected subharmonic signal. The phase noise of the injected subthreshold signal. Typically, the phase noise is far superior to that of a freely oscillating ring oscillator. .
[0030] The above-described embodiments further illustrate the purpose, technical solution, and advantages of the present invention. It should be understood that the above-described embodiments are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made to the present invention within the spirit and principles of the present invention should be included within the protection scope of the present invention.
Claims
1. A subharmonic injection-locked oscillator for a medical implantable communication system, characterized in that, It includes a single-ended injection inverter, an AC coupling capacitor, a ring oscillator, and a tail current source; the output terminal of the single-ended injection inverter is connected to one end of the AC coupling capacitor, and the other end of the AC coupling capacitor is connected to the ring oscillator; The ring oscillator is connected to the tail current source.
2. The subharmonic injection-locked oscillator for a medical implantable communication system according to claim 1, characterized in that, The ring oscillator comprises five single-ended inverters connected in series, with the output of the last single-ended inverter connected to the input of the first single-ended inverter; the sources of all five single-ended inverters are connected to the output of the tail current source.
3. The subharmonic injection-locked oscillator for a medical implantable communication system according to claim 1, characterized in that, The tail current source is a 32-bit thermometer-coded current source, consisting of 32 tail transistors connected in parallel. Each tail transistor has a switch at its gate and is connected to a bias voltage. The drains of the 32 tail transistors are connected and serve as the output terminals of the tail current source, which are connected to a ring oscillator. The sources of the 32 tail transistors are all grounded.
4. A subharmonic injection-locked oscillator for a medical implantable communication system according to claim 3, characterized in that, The drain-source voltage of the tail transistor in the tail current source is less than 50mV.
5. A subharmonic injection-locked oscillator for a medical implantable communication system according to claim 3, characterized in that, The dimensions of the tail transistor in the tail current source must meet the following requirements: ； ； in, This indicates the width-to-length ratio of the 0th tail transistor of the tail current source. This represents the width-to-length ratio of the nth tail transistor of the tail current source, where n is an integer from 0 to 31; This indicates the channel width of the tail transistor. This indicates the channel length of the tail transistor.
6. A subharmonic injection-locked oscillator for a medical implantable communication system according to claim 1, characterized in that, When the subharmonic injection locked oscillator is in use, a subharmonic signal is injected into the input terminal of its injection inverter.
7. A subharmonic injection-locked oscillator for a medical implantable communication system according to claim 6, characterized in that, The free oscillation frequency of the ring oscillator is: The injection frequency of the subharmonic signal is ; It is the frequency of the injected subharmonic signal, N is Integers.