R Reza Mahmoudi

A GSM/EDGE/WCDMA Adaptive Series-LC Matching Network Using RF-MEMS Switches

To preserve link quality of mobile phones, under fluctuating user conditions, an adaptively controlled series-LC matching circuit is presented for multi-band and multi-mode operation. Following a bottom-up approach, we discuss the design of an RF-MEMS unit cell for the construction of a 5-bit switched capacitor array. To reduce dielectric charging of the RF-MEMS devices their average biasing voltage is minimized by applying a bipolar waveform with a small high/low duty-cycle obtained from a high-voltage driver IC. RF-MEMS capacitive switches are applied because of their high linearity, low loss, large tuning range, and easy control in the discrete domain. Application specific RF-MEMS pull-in and pull-out voltage requirements are derived. An impedance phase detector is used to feed mismatch information to an up-down counter providing robust iterative control. The measured MEMS array capacitance tuning ratio is almost a factor 10. Module insertion loss is 0.5 dB at low-band and high-band. Harmonic distortion is less than -85 dBc at 35 dBm output power and the EVM, measured in EDGE-mode, is less than 1% at 27 dBm . The adaptively controlled module, connected to a planar inverted-F antenna, shows desired impedance correction. For extreme hand-effects the maximum module impedance correction at 900 MHz is -75jOmega.

Adaptive Impedance-Matching Techniques for Controlling L Networks

The link quality of mobile phones suffers from antenna mismatch due to fluctuating body effects. Techniques for adaptive control of impedance-matching L networks are presented, which provide automatic compensation of antenna mismatch. To secure reliable convergence, a cascade of two control loops is proposed for independent control of the real and imaginary parts of impedance. A secondary feedback path is used to enforce operation into a stable region when needed. These techniques exploit the basic properties of tunable series and parallel LC networks. A generic quadrature detector that offers a power-independent orthogonal reading of the complex impedance value is presented, which is used for direct control of variable capacitors. This approach renders calibration and elaborate software computation superfluous and allows for autonomous operation of adaptive antenna-matching modules.

Adaptive methods to preserve power amplifier linearity under antenna mismatch conditions

Under antenna mismatch conditions at high output power, voltage clipping (due to collector voltage saturation) is the main cause of power amplifier linearity degradation. To preserve linearity under mismatch three adaptive methods are presented that make use of the detected minimum collector peak voltage. This detected signal controls either the amplifier output power, load-line, or supply voltage. These concepts are generalized analytically, and calculated results compare well to simulations. Measurements demonstrate am error vector magnitude reduction of 5% and an adjacent channel power ratio improvement of 10 dB at a voltage standing wave ratio of 4 for an EDGE amplifier with adaptively controlled output power. These adaptive methods offer a cost and size effective alternative to the use of an isolator.

Analysis and Design of a 60 GHz Wideband Voltage-Voltage Transformer Feedback LNA

To cope with the problem of instability and imperfect reverse isolation, a millimeter-wave voltage-voltage transformer feedback low noise amplifier has been analyzed, designed, and measured in CMOS 65 nm technology. Analytical formulae are derived for describing the stability, gain, and noise in this circuit topology. An analogy with the classic concept of Masonss invariant is used to illustrate how the transformer feedback provides the required reverse isolation in the LNA. Based on the developed theoretical analysis, the circuit is implemented as a fully integrated 60 GHz two-stage differential low noise amplifier in 65 nm CMOS technology. A flat gain of 10 dB is achieved over the entire 6 GHz bandwidth. The measured noise figure is 3.8 dB.

RF-MEMS based adaptive antenna matching module

To preserve the link quality, in fluctuating operating environments, an adaptive antenna matching module is presented that consists of a 5-bit RF-MEMS switched capacitor array, a bipolar 60/30 V MEMS-biasing voltage generator for improved reliability, and an impedance phase detector that provides information on mismatch. It uses an iterative up-down counting algorithm for robust control. Measurements show proper correction of the antenna reactance, even for a VSWR of 10. The switched capacitor array exhibits a large tuning range from 1 to 15 pF and an insertion loss of 0.4 dB. The detector dynamic range equals 35 dB with an accuracy of 8 degrees from 0.8 to 2 GHz. Adaptive matching will make isolators redundant.

A Mismatch Detector for Adaptive Antenna Impedance Matching

The efficiency of a mobile phones power amplifier suffers from the antenna impedance mismatch caused by the body-effect of its user. A mismatch detector used for an innovative antenna matching algorithm which is based on adaptive correction of the reactive part of the antenna impedance mismatch has been designed, implemented and measured. The mismatch detector which consists of a wideband 90deg phase shifter, a limiter and a Gilbert-cell multiplier detects the phase of the reflection coefficient. The dynamic range of the mismatch detector is up to 142deg at the standard GSM frequencies (900MHz, 1800MHz and 1900MHz) for input power not less than -20dBm. This mismatch detector fulfills the function of determining the mismatch property according to the presented adaptive antenna impedance matching algorithm

A Ka Band, Static, MCML Frequency Divider, in Standard 90nm-CMOS LP for 60 GHz Applications

This paper presents a broadband, static, 2:1 frequency divider in a bulk 90 nm CMOS LP (low-power) technology with maximum operating frequency of 35.5 GHz. The divider exhibits an enhanced input sensitivity, below 0 dBm, over a broad input range of 31 GHz and consumes 24 mA from a 1.2 V supply. The phase noise of the divider is -124.6 dBc/Hz at 1 MHz offset from the carrier.

Power Amplifier Protection by Adaptive Output Power Control

Cellular phone power amplifiers (PAs) operate in strongly varying environments and have to withstand extreme conditions. To avoid destructive breakdown a generic protection concept is proposed that is based on adaptive control of the output power. It provides over-voltage, over-temperature, and/or over-current protection by detection of the collector peak voltage, die temperature, and/or collector current to reduce the effective power control voltage once a threshold level is crossed. By applying protections, PAs can be implemented in low-cost silicon technology competitively to GaAs HBT implementations. In addition, requirements on package thermal resistance are relaxed. In this paper a theoretical analysis is given on the behavior of a class-AB amplifier under mismatch conditions. Measurement results on a silicon bipolar power transistor with integrated protection circuits are presented, proving the concept of adaptive protection. For a supply voltage of 5 V and nominal output power of 2 W no breakdown is observed for a VSWR of 10 over all phases when output power is adaptively reduced by 2.7 dB at most.

Fully balanced 60 GHz LNA with 37 % bandwidth, 3.8 dB NF, 10 dB gain and constant group delay over 6 GHz bandwidth

This paper presents a two-stage fully integrated 60 GHz differential Low Noise Amplifier implemented in a TSMC bulk CMOS 65 nm technology. Implementation of a voltage-voltage feedback enables the neutralization of the Miller capacitance and the achievement of flat gain with a deviation of ± 0.25 dB over the entire 6 GHz bandwidth. It features a transducer gain (Gt) of 10 dB along with a noise figure (NF) of 3.8 dB, NFmin of 3.7 dB and a constant delay time. IIP3 is 4 dBm. It consumes 35 mW from a 1.2 V supply and only occupies 330 × 170 µm.

A new statistical approach for nonlinear analysis of limit cycle amplifiers

Limit cycle loops are becoming popular due to their potential for higher efficiency and linearity, as data convertors and/or amplifiers. Therefore the analysis of this architecture in different aspects is essential. In this paper a statistical orthogonalization based approach for analysis of limit cycle amplifiers, excited by a Gaussian random signal is developed and the advantages over conventional methods are discussed. The validity of the proposed approach is verified by comparison between the circuit envelope simulation and the results achieved from the proposed algorithm.