S. Heck

A 1.55 GHz to 2.45 GHz center frequency continuous-time bandpass delta-sigma modulator for frequency agile transmitters

This paper presents a 4th order continuous-time bandpass delta-sigma modulator (CT-BPDSM) with a programmable center frequency ranging from 1.55 GHz to 2.45 GHz. The modulator is suited to be applied in multi-standard class-S power amplifiers. The circuit features a multi-feedback architecture with return-to-zero (RZ) and half-return-to-zero (HRZ) pulses. The loop filters consist of LC-resonators with emitter degenerated input transconductors and Q-enhancement circuits. A configuration register allows to program the resonator input transconductors, the Q-enhancement circuits and the resonator capacitances with 5 bit resolution. Fine tuning of the resonator center frequency is achieved with varactors. The circuit is implemented in a 200 GHz-fT SiGe-bipolar technology. The measured SNR at 2.2 GHz center frequency is 45.5 dB in a bandwidth of 20 MHz. At 1.55 GHz the SNR decreases to 40.7 dB. The measured uplink UMTS-FDD ACLR (adjacent channel leakage power ratio) of the modulator output is 48.4 dB in the first adjacent channel.

A switching-mode amplifier for class-S transmitters for clock frequencies up to 7.5 GHz in 0.25µm SiGe-BiCMOS

This paper presents the first voltage mode H-bridge switching amplifier in a fast complementary SiGe-technology for frequencies in the GHz range. The amplifier is suited as a driver for a high power GaN amplifier in class-S transmitters. It can be operated with pseudo-random digital pulse trains up to 7.5 Gbit/s. The measured broadband output power for a rectangular drive signal with a 50% duty cycle and a frequency of 2 GHz is about 148 mW. The efficiency of the switching stage including its two-stage inverter driver is about 43%. Including the input current-mode-logic (CML) stage, the PAE is about 30%.

Continuous-Time Bandpass Delta-Sigma Modulator for a Signal Frequency of 2.2 GHz

A continuous-time bandpass delta-sigma modulator (CT BPDSM) for class-S power amplifier applications with a center frequency of 2.2 GHz is presented. Class-S amplifiers are considered to provide a very power efficient way to amplify signals with high dynamic range. The modulator has a multi-feedback architecture. It features a low noise transconductor with series emitter degeneration, tunable LC resonators with Q-enhancement and an optimized clock tree operating at 7.5 GHz. The circuit is implemented in a 200 GHz-fT SiGe-bipolar technology. A peak SNDR of 43 dB in a bandwidth of 20 MHz is measured. The circuit dissipates 450 mW from a 3.6 V supply.

Power supply modulation for RF applications

Envelope tracking is a promising means to enhance radio frequency power amplifier efficiency for signals with non-constant envelope. The adaption of the power amplifier supply voltage is performed by a voltage modulator circuit, which is mainly based upon power electronics circuits, but requires bandwidths up to the MHz region. This paper introduces the benefits and challenges of envelope tracking and gives an overview of several voltage modulator architectures. Current measurement data of a class-G modulator is presented as well.

Efficiency of Current-Mode Class-D Amplifiers with Delta-Sigma Modulated Drive Signals

This paper describes the losses and efficiency deteriorations due to several non-idealities of a current-mode class-D amplifier driven by a Delta-Sigma pulse sequence. The computation of the total efficiency of the amplifier is presented. Finally the results are verified by designing and measuring an amplifier driven by a pulse sequence with 50 % duty cycle and a frequency of 30 MHz. The measured efficiency of 55.6 % fits the calculated value of 58.3 %.

A 1.6 GHz switch mode power amplifier with continuous-time bandpass delta-sigma modulator

A continuous-time bandpass delta-sigma modulator (CT BDSM) is designed and fabricated in a SiGe bipolar transistor technology with a transit frequency of 200 GHz. The modulator can be tuned in its center frequency from 1.55 GHz up to 2.45 GHz for mobile base station applications. To drive a GaN high power amplifier a driver amplifier is presented using a complementary bipolar transistor technology.

A high gain SiGe-GaN switching power amplifier in the GHz-range

This paper reports a GaN switching power amplifier with a complementary SiGe driver stage in a hybrid setup. The gain of the overall amplifier module is higher than 40 dB. Drain efficiency and an overall lineup efficiency of 60 % and 47 % respectively could be achieved at a bit rate of 1 Gbps when operating with a periodic drive signal. An operation up to 4 Gbps using a pseudo random pulse sequence is demonstrated. To the authors knowledge, this is the first time a GaN switching amplifier with a SiGe driver is demonstrated. Furthermore, such a high gain combined with the efficiencies at bit rates above 1 Gbps has not been presented yet.

Comparison of a single and a dual-gate GaN switching-amplifier for future communication systems

A high efficiency switch-mode amplifier with a dual-gate configuration in the output stage is designed in a 250 nm GaN HEMT technology. Measurements are performed up to 8 Gbps using periodic square wave signals and bandpass delta sigma (BPDS) signals. The results are compared to a single-gate amplifier which uses the same driver stage and gate width. The dual-gate amplifier achieves a higher output power and shows a better RF-performance at bit rates above 2 Gbps. A broadband output power of 14 W and a PAE of 77.5 % at 0.9 Gbps are demonstrated. Furthermore, a 5.2 Gbps BPDS signal with an eye amplitude of about 50 V is measured. It is the first time that such high amplitudes are achieved in combination with bit rates above 5 Gbps. The presented measurement results demonstrate the importance of GaN devices for future switch-mode amplifiers.

A high-power dual-gate GaN switching-amplifier in the GHz-range

A high efficient GaN switch-mode amplifier for Gbit data rates is presented. The design uses GaN HEMTs with a gate length of 250 nm. It consists of a dual-gate transistor configuration in the output stage. This allows an increase of supply voltage in order to increase the output power. If an increase of power is not required, device size can be reduced which comes along with a better RF-performance. The presented amplifier exhibits an output signal with peak-to-peak voltages up to 60 V and achieves a broadband output power of 17 W with a PAE of 79.5 % at 0.9 Gbps. Considering a bit rate of 5.2 Gbps, the corresponding values are 40 V, 4 W and 38.6 %. To the authors knowledge, the presented amplifier is the first GaN switch-mode amplifier with a dual-gate transistor in the output stage. Its measured results are the best concerning the combination of a high frequency and a high power at the same time.