Digital Frequency Tuning Research Articles

Extended cavity quantum cascade laser with cavity resonator integrated grating filter.

We report on an extended cavity quantum cascade laser based on a cavity resonator integrated grating filter (CRIGF) that acts as both cavity end-reflector and spectral selector. Stable, mode-hop free, single-mode emission around 2150 cm-1 is obtained over large injection current ranges (more than 50 mA) with a typical threshold around 290 mA. A digital frequency tuning over more than 65 cm-1 is obtained by changing the periodicity of the CRIGF ending the extended cavity.

Continuous‐time filter featuring Q and frequency on‐chip automatic tuning

AbstractThe on‐chip automatic tuning of digitally programmable continuous‐time Gm‐C filters with a wide operation range employing a hybrid analog‐digital master‐slave scheme is reported in this work. The master system is implemented with a voltage‐controlled filter (VCF) with the same programmable transconductance cells as the main filter to enhance the matching between master and slave. The frequency tuning method, for both analog and digital control, is based on a digital phase comparator included in the phase‐locked loop achieving high‐precision tunability. The digital frequency tuning is obtained with an error of ±4% and the maximum settling time when changing between two consecutive digital words is 0.3 µs. Once the digital word is fixed, the analog tuning finely adjusts the value of the characteristic frequency to the reference and corrects for possible temperature variations with a settling time of 0.2 µs. The analog frequency control covers the whole discrete step with a maximum error of ±5%. Furthermore, a magnitude‐locked loop (MLL) Q‐tuning block is simultaneously applied to the system in order to precisely control the quality factor of the Gm‐C filter by using an appropriate envelope detector. According to the obtained results, both post‐layout simulation and experimental results, the adopted scheme has resulted as a useful and adequate solution to implement the complete auto‐tuning system of digitally programmable continuous‐time filters, including frequency and Q‐control. Copyright © 2008 John Wiley & Sons, Ltd.

A 12-mW 264-MHz high linearity sharp roll-off CMOS opamp-RC low-pass filter for MB-OFDM UWB systems

This paper presents a high linearity wideband sharp roll-off Opamp-RC low-pass filter (LPF) for Ultra wideband (UWB) applications. The proposed LPF is composed of three biquads’ transfer functions with different Q-factors in series. Sharp roll-off is attributed to the steep slope of the peaking of a biquad transfer function with a high Q-factor. The superposition of these biquads also helps extend the bandwidth of the overall LPF transfer function without the cost of extra power dissipation. The effects of biquad arrangements on noise and linearity performances are investigated. A simple operational amplifier (op-amp) is adopted to ensure high frequency characteristics and high linearity performance for the designed filter. The LPF is implemented in 0.13-μm IBM CMOS process from 1.5 V supply. The measured cutoff frequency is 264 MHz with the pass-band ripple of less than 1 dB. Digital frequency tuning is implemented with 40% of tuning range around the cutoff frequency. The amount of out-of-band rejection at 290 MHz and at twice cutoff frequency is 12 dB and about 50 dB, respectively. Good linearity with IIP3 of 23 dBm is obtained. The 6th-order LPF dissipates only 12 mW with the active chip size of 400 × 640 μm2.

Current-Division-Based Digital Frequency Tuning for Active RC Filters

This manuscript presents a novel digital frequency tuning technique for integrated active RC filters. Unlike the traditional tuning approach of varying the values of the capacitors or resistors, the proposed technique achieves the tuning by varying the currents that flow through the resistors or capacitors. In this manuscript, the current varying is achieved by using a digital-controlled MOSFET-only current division network. This new tuning technique features digital tuning, compact size, and wide tuning range as well as high linearity as demonstrated by transistor-level circuit simulations.

Digital frequency tuning technique based on current division for integrated active RC filters

A novel digital frequency tuning technique is presented for integrated active RC filters. Instead of varying the values of the capacitors or resistors as in traditional approaches, the proposed technique achieves frequency tuning by dividing the currents that flow from resistors to virtual grounds. Current division is performed through a digitally programmable current division network added at each virtual ground. The technique features compact size, wide tuning range and high linearity. Transistor level simulation results are presented to demonstrate the technique.