This Letter presents a low-residual-offset second-order sigma-delta modulator. By inserting a chopper working at low frequency to the mirrored integrator at the first stage of the modulator, the original residual offset is transferred to a high frequency, which can be removed by the filter. Besides, by applying the second-order fractal sequence as the timing of the new added chopper, the residual offset accumulation problem due to the integration at the second stage can be avoided. To evaluate the effect of residual offset suppression conveniently, a programmable timing is integrated to the design to control the state of the added chopper. The presented modulator is fabricated in a 0.18 um CMOS technology, the core area of which is 0.38 mm². Based on the measurement results, the DC offset of the sigma-delta modulator with the proposed method is reduced by 85.6 µV. The modulator realizes 64.8 dB dynamic range with 1 MHz sampling rate, which consumes 0.96 mW from a 3.3 V supply.

A novel power-efficient analog buffer at Liquid Helium Temperature (LHT) is proposed. The proposed circuit is based on an input stage consisting of two complementary differential pairs to achieve rail-to-rail level tracking. Results of simulation based on SMIC 0.18µm CMOS technology show the high driving capability and low quiescent power consumption at cryogenic temperature. Operating at single 1.4 V supply, the circuit achieves a slew-rate of +36 V/µs and -33.8 V/µs for 10 pF capacitive load. The static power of the circuit is only 55.7µW.

A new measurement method is proposed in this letter to improve the accuracy of electromagnetic parameters measurement with air coaxial line, especially in low frequency band. The new method measures reflection parameters of the air coaxial line with terminal short-circuited and open-circuited, then the impedances from the specimen section to terminal are calculated. Combined with the impedance equations established based on the transmission line theory, the complex permittivity and complex permeability of the specimen are derived. Compared with the classic Nicolson-Ross-Weir (NRW) method, the method proposed achieves better accuracy in low frequencies, which is proved in this letter through comparative measurements.

This paper presents a self-packaged Gysel power divider (PD) with embedded metamaterials in substrate integrated suspended Line (SISL) platform. Metamaterials are formed by a periodic arrangement of I-shaped electrical resonators that can produce high dielectric constants and are encapsulated in the multi-layer SISL structure to reduce the circuit size. Fabricated by using a standard printed circuit board (PCB) process, the proposed Gysel PD is self-packaged. The structure of the meandering line introduced in the layout of PD can be downsized. The designed PD with embedded metamaterials operates from 3.3 to 3.6 GHz with a bandwidth of 14.8% for S₁₁ < -20 dB. Compared with the case where metamaterials are not embedded, the circuit area is reduced by about 61%.