Zihui Zhang

Analysis and characterization of microstrip structures up to 90 GHz in SiGe BiCMOS

In this work electromagnetic analysis and experimental verification of integrated microstrip transmission lines on silicon substrates have been performed up to 90 GHz. Several microstrip lines of different width and length have been realized on a five metal layer silicon substrate together with a commercial SiGe HBT process. All structures have been analyzed using a 2.5D electromagnetic simulation environment. The results of the EM simulation are compared with measurements. De-embedding techniques have been applied on the measured results to remove probe pad and other parasitic effects. Line parameters like characteristic impedance, propagation constant and effective permittivity are determined from de-embedded structures. The dependency of these quantities on various design parameters will be presented.

Lumped Element MIM capacitor model for Si-RFICs

This work describes a lumped element based MIM capacitor model for the frequency range up to 110 GHz. Several MIM capacitors with different areas have been fabricated in a five metal layer 0.25 m SiGe HBT technology. All structures have been analyzed in a 2.5 D EM simulation environment and the simulated results are compared to measurements. A lumped element model valid up to 110 GHz has been developed based on curve fitting techniques. Good agreements with measurements have been achieved up to 110 GHz. Finally, the extracted model parameters suitable for the entire frequency range are tabulated.

Lumped Element Coplanar-Microstrip-Transition Model for Si-RFICs up to 90 GHz

The development of a lumped element model for monolithic integrated transitions from coplanar probe pads to microstrip line structures is presented for a frequency range up to 90 GHz. Several passive test structures have been fabricated in a five metal layer SiGe BiCMOS process technology. The values of the lumped elements are determined based on measurements and are tabulated in this work. In order to verify the performance of the proposed transition model, comparisons with measurements of known structures are carried out.

Highly efficient and wideband harmonically tuned GaN-HEMT power amplifier

In this paper, the design of a highly efficient 25 W GaN-HEMT power amplifier (PA), operating in 1.7 - 2.3 GHz, is presented. The influence of the harmonics and the impact of the parasitic components of the nonlinear device are considered in order to ensure an accurate matching network design to achieve high efficiency. Optimum fundamental and harmonic load impedances were obtained using load-pull simulations across the operation band. From continuous wave large-signal measurements, an average output power of 44 dBm was obtained over the bandwidth. The corresponding drain efficiency ranged between 73 - 80 % with a gain of 12 dB. Linearized modulated measurement, using 10 MHz LTE signal with 7.3 dB peak-to-average-power-ratio (PAPR), shows an average power-added-efficiency (PAE) of 38.2 % and adjacent channel leakage ratio (ACLR) of almost -45 dBc at 1.8 GHz.

A Novel Design Approach for Highly Efficient Multioctave Bandwidth GaN Power Amplifiers

This letter presents a novel approach to design highly efficient multioctave bandwidth power amplifiers (PAs). The fundamental load impedances are slightly detuned out of their optimum values to reduce the in-band harmonics influence on output power and power-added efficiency. The design of the output matching network includes a 4:1 planar Guanella transformer for wide bandwidth and low complexity. In the frequency band 0.5–2.7 GHz, the PA achieves 9.2 ± 1.2 dB power gain and more than 20-W output power. The drain efficiency varies from 56% to 70% over the bandwidth.

A novel structure of high directivity broadband microstrip coupler

This work describes two methods for improving the directivity of an edge coupled microstrip based coupler with weak coupling. The proposed couplers have a coupling factor of about -30 dB. The coupler with interdigital capacitors achieved for excess loss of 0.5 dB a fractional bandwidth of 44 % and directivity of 25 dB. The second structure uses floating stubs between the coupled lines, which increases the fractional bandwidth up to 67% with the same directivity. The insertion loss of the proposed structures is lower than 0.3 dB.

Ultra-broadband GaN power amplifier utilizing planar Guanella transformer

In this work, the design concept of a highly efficient and ultra-broadband GaN power amplifier is presented. The amplifier uses a novel concept for realizing the impedance matching networks with multi octave bandwidth. These matching networks are based on planar, broadside coupled micro-strip lines that are interconnected to a 4:1 Guanella impedance transformer. To achieve an even mode impedance as high as possible, the ground metallization underneath the coupled lines is removed. A high even mode impedance is the key for achieving wide bandwidth. The designed amplifier, deploying a commercial 25 W GaN HEMT from CREE™ achieved a CW output power of more than 42 dBm over a frequency range from 0.4 to 2.8 GHz with a minimum PAE of 45% over the whole bandwidth and peak PAE-values of more than 65%.

Characterization of high voltage varactors for load modulation of GaN-HEMT power amplifier

In this work, a semiconductor varactor and a ferroelectric varactor, used for designing load modulation power amplifiers, are compared. The semiconductor varactor shows considerable advantages in terms of tuning range, tuning voltage, tuning speed, and losses in comparison to the ferroelectric varactor, which was a thick-film Barium Strontium Titanate (BST) device. A fixed matching network power amplifier (FMN-PA) was fabricated in order to enable comparisons with a previously designed tunable matching network (TMN) load modulation PA based on BST. Both PAs are driven in class C, operate at 1.8 GHz and use a GaN HEMT. The maximum measured drain efficiencies for the FMN-PA and TMN-PA are 79 % and 69 % at the maximum output power of 43 dBm. At 6 dB back-off output power the efficiencies are 45% and 62% respectively, after controlling the bias voltage for the TMN case. Better performance for the TMN-PA is achievable using the semiconductor varactor according to the obtained characterization results of this work.

Linearity analysis of class-B/J continuous mode power amplifiers using modulated wideband signals

Linearity, along with efficiency and bandwidth, belongs to the fundamental requirements of power amplifiers for nowadays communications systems. This paper discusses how to bring together these partly contradictory goals in power amplifier design. Continuous class-J PAs provide a constant efficiency over a large bandwidth. However, the linearity is not constant due to the unequal current and voltage waveforms along the design space of the continuum. Nevertheless, it is possible to equalize linearity of such a PA over the desired bandwidth. For the PA presented, -50 dBc ACLR with an average power of 38 dBm and an average efficiency of 21.5 % were achieved at 2.14 GHz using a WCDMA test signal. For CW measurements, 48.5 dBm maximum power and 63 % peak drain-efficiency were reached.