Subharmonic Injection Locking Research Articles

Frequency tunable CMOS ring oscillator‐based Ising machine

SummaryOscillator‐based Ising machines (OIMs) particularly those realized in complementary metal oxide semiconductor (CMOS) have gained popularity for solving combinatorial optimization problems (COPs) in recent years due to its scalability, low‐power consumption, and room temperature operation. The implemented OIMs have thus far focused on solving optimization problems with a single global minima. However, real‐life optimization problems often have multiple solutions. In this paper, we propose a generalized approach to solve COPs with single (without contention), as well as multiple (with contention) solutions using frequency tunable CMOS ring oscillator (ROSC)‐based Ising machine. A capacitive frequency tunable CMOS ring‐oscillator coupled with an internal subharmonic injection locking (SHIL) generator realized using 14‐nm FinFET models works as Ising spin in the proposed approach. We demonstrate how frequency tuning can help in attaining good quality results and also determine all possible solutions of COP with contention. We also propose a generalized algorithm for monitoring the states of the oscillator network to indicate tuning necessity and extract solutions from the oscillator's output irrespective of the type of COP.

Parametric Frequency Divider Based Ising Machines.

We report on a new class of Ising machines (IMs) that rely on coupled parametric frequency dividers (PFDs) as macroscopic artificial spins. Unlike the IM counterparts based on subharmonic-injection locking (SHIL), PFD IMs do not require strong injected continuous-wave signals or applied dc voltages. Therefore, they show a significantly lower power consumption per spin compared to SHIL-based IMs, making it feasible to accurately solve large-scale combinatorial optimization problems that are hard or even impossible to solve by using the current von Neumann computing architectures. Furthermore, using high quality factor resonators in the PFD design makes PFD IMs able to exhibit a nanowatt-level power per spin. Also, it remarkably allows a speedup of the phase synchronization among the PFDs, resulting in shorter time to solution and lower energy to solution despite the resonators' longer relaxation time. As a proof of concept, a 4-node PFD IM has been demonstrated. This IM correctly solves a set of Max-Cut problems while consuming just 600 nanowatts per spin. This power consumption is 2 orders of magnitude lower than the power per spin of state-of-the-art SHIL-based IMs operating at the same frequency.

How Frequency Injection Locking Can Train Oscillatory Neural Networks to Compute in Phase.

Brain-inspired computing employs devices and architectures that emulate biological functions for more adaptive and energy-efficient systems. Oscillatory neural networks (ONNs) are an alternative approach in emulating biological functions of the human brain and are suitable for solving large and complex associative problems. In this work, we investigate the dynamics of coupled oscillators to implement such ONNs. By harnessing the complex dynamics of coupled oscillatory systems, we forge a novel computation model-information is encoded in the phase of oscillations. Coupled interconnected oscillators can exhibit various behaviors due to the strength of the coupling. In this article, we present a novel method based on subharmonic injection locking (SHIL) for controlling the oscillatory states of coupled oscillators that allow them to lock in frequency with distinct phase differences. Circuit-level simulation results indicate SHIL effectiveness and its applicability to large-scale oscillatory networks for pattern recognition.

Oscillatory Neural Networks Using VO2 Based Phase Encoded Logic.

Nano-oscillators based on phase-transition materials are being explored for the implementation of different non-conventional computing paradigms. In particular, vanadium dioxide (VO2) devices are used to design autonomous non-linear oscillators from which oscillatory neural networks (ONNs) can be developed. In this work, we propose a new architecture for ONNs in which sub-harmonic injection locking (SHIL) is exploited to ensure that the phase information encoded in each neuron can only take two values. In this sense, the implementation of ONNs from neurons that inherently encode information with two-phase values has advantages in terms of robustness and tolerance to variability present in VO2 devices. Unlike conventional interconnection schemes, in which the sign of the weights is coded in the value of the resistances, in our proposal the negative (positive) weights are coded using static inverting (non-inverting) logic at the output of the oscillator. The operation of the proposed architecture is shown for pattern recognition applications.

Subharmonic Injection Locking for Phase and Frequency Control of RTD-Based THz Oscillator

Phase and frequency control of resonant tunneling diode (RTD) based terahertz oscillators are major challenges in realizing coherent signal sources for arrayed applications, such as spatial power combining, beam steering, or multi-in multi-out systems. In this letter, we demonstrate frequency locking and control of an RTD oscillating at f 0 ∼ 550 GHz, via radiative injection of a weak sinusoidal subharmonic signal at f 0/2. Precise frequency control, within the locking range of around 2 GHz, is demonstrated. A peak output power enhancement of 14 dB in the whole locking range, compared to the free running oscillator, is achieved. Furthermore, occurrence of phase locking is identified by the spectral linewidth reduction, quantifiable in the full-width at half-maximum parameter. A signal linewidth of 490 Hz was achieved in locked operation.

A Multi-Phase Sub-Harmonic Injection Locking Technique for Bandwidth Extension in Silicon-Based THz Signal Generation

This paper presents a multi-phase sub-harmonic injection locking technique. This technique can significantly increase the locking range of a multi-phase injection locking oscillator compared to the conventional single-phase injection locking scheme. By application of this technique, a scalable “active frequency multiplier” chain architecture is proposed, which can generate THz signal from a low mm-wave frequency or RF reference source. We also propose a multi-ring system topology to implement this frequency multiplier scheme. As proof of concept, a cascaded 3-stage 3-phase 2nd-order sub-harmonic injection locking oscillator chain is implemented in the IBM9HP SiGe BiCMOS process with its $f_{\rm T}/f_{\max}$ of 300/350 GHz. The design achieves a maximum output power of $-$ 16.6 dBm at 498 GHz, a phase noise of $-$ 87 dBc/ Hz at 1 MHz offset, and a total 5.1% frequency tuning range from 485.1 GHz to 510.7 GHz, which is the largest frequency tuning range among all the reported silicon-based THz oscillator sources in the 0.5 THz band.

Frequency-Hopped Quadrature Frequency Synthesizer in 0.13-$\mu$m Technology

This paper presents a Wireless-USB/WiMedia-compliant fast-hopping frequency synthesizer architecture with quadrature outputs based on sub-harmonic injection-locking. The synthesizer features a cross-coupled quadrature digitally-controlled oscillator, that is injection-locked to a sub-harmonic frequency. An intuitive closed-form expression for the dynamics of the quadrature injection-locked oscillator and a technique to achieve fast frequency-hopping, are presented. The overall architecture, based on this technique, is a CMOS-only implementation and has been fabricated in a 0.13-μm SiGe BiCMOS process. On-chip mixers have been implemented to measure the quadrature accuracy of the outputs. Measurement results indicate lock-times of less than 2.5 ns, a locked phase noise of -114 dBc/Hz at 1 MHz offset and a quadrature accuracy of better than 0.5°. The frequency synthesizer (excluding output buffers) occupies an area of 0.27 mm2 and consumes 14.5 mW of power. The best and worst case spur suppression achieved are 47 and 31 dB, respectively. This is the lowest power fast-hopping quadrature frequency synthesizer that has been reported to date.

Application of Subharmonic Injection Locking of LC Oscillators to LO-Based Phase-Shifting Phased-Array Architectures

A ninth-subharmonic injection-locking scheme is proposed for local oscillator (LO) phase-shifting-based phased-array architectures operating in the ISM band at 24 GHz. The presented architecture employs a phase-shifter at the ninth subharmonic, a high-speed regenerative comparator, and a negative-gm oscillator to synthesize multiple phases of ninth-harmonic LO signals from a 2.41-GHz reference at the destination and in close proximity to the RF/millimeter-wave front-end mixers with first LO at 21.69 GHz. A digital phase-shift calibration technique is discussed. The reported LO phase-shifting and synthesis scheme is implemented in IBM's 130-nm CMOS technology and consumes a total of 32 mA per LO element from a 1.2-V supply. The injection-locked oscillators have a phase-noise performance of - 107.17 dBc/Hz at 1-MHz offset from 21.51 GHz. The maximum phase-shift error at 21.69 GHz is 9.86° and 2.1° before and after calibration, respectively.

Subharmonic injection-locking and self-oscillating mixing

Subharmonic injection-locking and self-oscillating mixing functions of a modified Colpitts oscillator operating at 1GHz are reported. The injection-locking circuit, using a GaAs FET, is described t...

UWB Fast-Hopping Frequency Generation Based on Sub-Harmonic Injection Locking

Sub-harmonic injection locking is employed to generate the fast-hopping carriers required in UWB systems for WiMedia . A very small area 90-nm CMOS prototype synthesizes the frequencies of band group #6 with a hop time shorter than 4 ns . It occupies 0.074 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and draws 30 mA from a 1.2 V supply. Phase noise at 8.71 GHz is -112 dBc/Hz at 1 MHz offset. The design is supported by a thorough analysis that emphasizes the tradeoffs in the parameters of the proposed system.

A New Transponder Architecture With On-Chip ADC for Long-Range Telemetry Applications

We present a new architecture for wireless power and data telemetry that recovers power and a system clock from a weak incident RF signal. A high-efficiency RF-DC converter generates a 3-VDC supply for the system from a -12.3-dBm incident RF signal, gathered by a commercial 50-/spl Omega/ antenna. A system clock is extracted from the same incident signal, by an injection-locked LC oscillator. Sub-harmonic injection-locking facilitates the separation of the incident and the transmit signal frequencies, without need for a PLL. The proposed architecture is used in a long-range telemetry device, incorporating an on-chip ADC, and employing active telemetry for data transmission. Data is transmitted through binary phase-shift-keying of a 900-MHz carrier. The prototype, implemented in 0.25-/spl mu/m CMOS, occupies less than 1 mm/sup 2/. A wireless operation range of more than 18 meters is indicated by anechoic chamber testing.

High Effective Subharmonic Injection Locking of a Millimeter-Wave IMPATT Oscillator

Abstract-Effective stabilization of an IMPATT oscillator in the millimeter-wave region can be achieved through subharmonic injection locking to a weak parasitic oscillating signaI. In subharmonic injection-Iocking experiments more than 19 dB of locking gain at 10-MHz locking range was obtained at a subharmonic ratio 1:2 of the main oscillating frequency. At the subharmonics 1:4 and 1:6, the locking gain was more than 12 and 13 dB at 10 MHz, respectively. Using the parasitic oscillating signal, higher than 32-dB gain and 10-MHz locking range at a subharmonic ratio 1:2 of the parasitic oscillating frequency was obtained. This locking gain was 13 dB higher than that for the main oscillating signal. At the subharmonic ratio 1:4, the gain was more than 15 dB higher. As measured with the spectrum analyzer, the oscillating signal which was locked by the subharmonic injection signal almost coincided with the injection signal. These data show that the subharmonic injection locking has high gain as compared with that using the main oscillating signal.

Basic Properties of Subharmonic Injection Locking

Basic properties of subharmonic injection locking, as well as differences between subharmonic and fundamental injection locking, are studied with the describing function technique. The consequences of including a nonlinear capacitance as well as linear frequency-dependent parameters in the active element is investigated. The importance of the broad-band characteristics of the tuning circuit is studied. The detailed analysis is given for locking to the third subharmonic, but necessary expressions for generalizing the treatment to other than third subharmonic locking are provided. Finally, a note on stability of subharmonic locking is given.