Ankush Goel

Frequency Switching in Dual-Resonance Oscillators

An oscillator with a high-order (>2) resonator has multiple stable modes of oscillations. The stable modes for one such oscillator, having a fourth-order resonator, are found using a nonlinear analysis. By using a proper nonlinear active topology and tank component values, the fourth-order oscillator can generate either of the two distinct frequencies f1 or f2. A method is introduced to dynamically switch between the stable modes of oscillations. It is shown that the phase noise of this fourth-order oscillator, when generating only one of its resonant frequencies, is comparable to the phase noise of a second-order oscillator using the same active topology and resonator quality factor. Furthermore, the fourth-order oscillator has better phase noise and/or higher tuning range in VCO implementations compared to the commonly used switched resonator oscillators. The claims have been verified experimentally through an integrated oscillator prototype with f1 = 2.4 GHz and f2 = 4.7 GHz fabricated in a standard 0.18 mum CMOS technology. The oscillator draws 1.89 mA current of 1.8 V supply. The 1 MHz offset phase noises of the fourth-order oscillator for f1 = 2.4 GHz and f2 = 4.7 GHz are -122.4 dBc/Hz and -123.4 dBc/Hz, respectively.

A 24.7dBm all-digital RF transmitter for multimode broadband applications in 40nm CMOS

Recently, digitizing RF circuits has attracted extensive attention by exploiting high speed transistors offered in nano-scale CMOS processes. The digitally-assisted or digital-intensive RF transceivers not only benefit from technology scaling in terms of power efficiency and die area, but also improve functional flexibility. The polar architecture is well recognized for digital RF transmitters [1,2,4,5], while the bandwidth expansion resulting from Cartesian-to-polar transformation makes it difficult to comply with high-speed wireless standards. Open-loop phase interpolation topology was employed in an outphasing transmitter [3], where 12dBm output power was demonstrated with 40MHz 802.11n signal. In this work, an all-digital RF transmitter with direct quadrature architecture is presented to address the need for broadband wireless connectivity.

A 130-nm CMOS 100-Hz–6-GHz Reconfigurable Vector Signal Analyzer and Software-Defined Receiver

A monolithic 100-Hz-6-GHz reconfigurable vector signal analyzer (VSA) and software-defined receiver (SDR), following a two-step up-down conversion heterodyne scheme with robustness to various wideband interference scenarios and local oscillator (LO) harmonic mixing, is presented. The 130-nm CMOS chip does not require external filters or baseband processing to reduce the effect of interferences or LO harmonics. The receiver has tunable gain from -67 to 68 dB in steps of 0.5 dB, and tunable bandwidth from 0.4 to 11 MHz in steps of 0.5 MHz. The receiver sensitivity at the maximum gain is - 82 dBm. A monolithic VSA/SDR enables various commercial and military wireless solutions.

Concurrent Dual-Frequency Oscillators and Phase-Locked Loops

A dual-frequency oscillator employing a fourth-order tank is shown to have the ability to generate simultaneous oscillations at two frequencies. A nonlinear analysis to determine the steady-state and transient behavior of this oscillator is presented. Further, the phase-noise expression for the dual-frequency oscillator is derived and compared with that of a single-frequency oscillator. A dual-loop phase-locked loop (PLL) is designed to lock the frequencies of the dual-frequency oscillator to two external references independently. A prototype of a dual-frequency voltage-controlled oscillator (VCO) along with the dual-loop PLL is implemented in a BiCMOS SiGe technology. The dual-frequency VCO oscillates simultaneously at 2.33 and 4.98 GHz with 12.5% and 10.3% tuning ranges, respectively. The PLL has locking ranges of 4.2% and 3.6% for 2.33 and 4.98 GHz, respectively. Potential applications of concurrent multifrequency oscillators in multifunctional communication systems and multiband beam forming are discussed.

Tunable Duplexer With Passive Feed-Forward Cancellation to Improve the RX-TX Isolation

The paper presents an approach that enables trading off the insertion loss versus isolation in the duplexer design. Specifically, the Insertion Loss (IL) of the duplexer filters is reduced by using low-order Bandpass Filters (BPF), while the transmitter (TX) to receiver (RX) isolation is improved using a feed-forward, passive, wideband, cancellation scheme. The proposed cancellation scheme is fully passive and hence the duplexer does not incur power consumption and noise penalties. The linearity of the proposed duplexer is very high limited only by the tunable passive components used in the design. A tunable duplexer prototype is demonstrated with TX-RX isolation better than 50 dB in both TX and RX bands (high band TX: 860-890 MHz, RX: 948-984 MHz; low band TX: 700-718 MHz, RX: 780-801 MHz). Tuning is achieved using digitally controlled switched capacitors with silicon on sapphire (SOS) switches resulting in high linearity.

Semiconductor laser phase-noise cancellation using an electrical feed-forward scheme

We demonstrate the reduction of semiconductor laser phase noise by using an electrical feed-forward scheme. We have carried out proof-of-concept experiments on a commercially available distributed-feedback laser emitting at the 1550 nm communication band. The preliminary results show more than 20 times reduction in the phase-noise power spectrum. The feed-forward scheme does not have the limited bandwidth, stability, and speed issues that are common in feedback systems. Moreover, in the absence of electronic noise, feed-forward can completely cancel the close-in phase noise. In this scheme, the ultimate achievable phase noise will be limited by the electronics noise. Using the proposed feed-forward approach, the linewidth of semiconductor lasers can be reduced by 3-4 orders of magnitude in a monolithic approach using todays low-noise scaled transistors with terahertz gain-bandwidth product.

Injection Locking in Concurrent Dual-Frequency Oscillators

In a separate paper, the authors show that a nonlinear active core with a fourth-order resonator can generate two stable independent frequencies simultaneously. In this paper, the effect of injecting two frequencies into such a concurrent dual-frequency oscillator is analyzed and experimentally verified. It is shown that, for weak injection, the effect of injection at one frequency is decoupled from the effect of injection at the other frequency. The differential equation describing the effect of injection at either of the two frequencies is similar to the Adlers injection-locking equation for single-frequency oscillators. A theoretical analysis for a linear array of coupled concurrent dual-frequency oscillators is provided. It is shown that a linear phase progression at both frequencies can be achieved independently by detuning the arrays end elements. Dual-frequency quadrature signal generation using two coupled concurrent dual-frequency oscillators is also demonstrated. To verify the theoretical derivations, an integrated circuit in a 0.18-m SiGe BiCMOS process is designed and fabricated. Measurement results closely match the theoretical predictions. The application of concurrent coupled oscillator array in dual-frequency beam forming with steering capability is also demonstrated.

Active cancellation of acoustic noise using a self-tuned filter

In an increasingly noisy society, methods of reducing noise are becoming more important. This work proposes an analog electroacoustic circuit for active control of narrow-band low-frequency acoustic noise using adaptive filtering techniques. The circuit aims at producing antinoise, which is acoustically added to the disturbing noise to produce an error signal that is fed back to the circuit. The proposed circuit is a modified Kerwin-Huelsman-Newcomb biquad filter that tunes itself to the incoming noise frequency using the zero tuning techniques. The circuit was implemented on a printed circuit board and it was successful in reducing noise by 15-20 dB in open space. Active noise control specifically for narrow-band noise cancellation using adaptive analog filters seems to be a better solution than its digital signal processing counterpart in speed, cost, and robustness.

A 130nm CMOS 100Hz–6GHz reconfigurable Vector Signal Analyzer and Software-Defined Receiver

A monolithic 100Hz–6GHz reconfigurable Vector Signal Analyzer (VSA) and Software Defined Receiver (SDR), following a two-step up-down conversion heterodyne scheme with robustness to various wide-band interference scenarios, is presented. The 130nm CMOS chip does not require external filters or baseband processing to reduce the effect of interferences or harmonics. A monolithic VSA/SDR enables various commercial and military wireless solutions.

Phase noise in a synchronized concurrent dual-frequency oscillator

The phase noise in synchronized concurrent dual-frequency oscillators is analyzed. Two cases are considered -synchronization to external injection sources and synchronization in array of coupled identical oscillators. For small injection strengths, the phase noise behavior of synchronized concurrent dual-frequency oscillators at either of the frequencies is similar to that of synchronized single frequency oscillators. The phase noise of an injection locked concurrent dual-frequency oscillator for either of the frequencies follows the phase noise of external injection near that frequency for offsets within the locking bandwidth of the injection. For offsets outside of the locking bandwidth, the injection locked oscillators phase noise is equal to that of free running case. In the system of two coupled concurrent dual-frequency oscillators with bilateral coupling, the phase noise at either frequency is 3dB smaller than that at the free running case for offsets smaller than the locking bandwidth. Measurement results show a good match with the theory.