A CMOS power amplifier in nanometer technology for portable applications
In recent years, the demand for the battery-powered devices has been increasing rapidly. At the same time, the requirements for the audio power amplifier (APA) also extend to hi-fi quality music playback. In order to achieve high run time per charge for the portable devices, the quiescent power c...
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Format: | Theses and Dissertations |
Language: | English |
Published: |
2016
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Online Access: | https://hdl.handle.net/10356/69246 |
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Institution: | Nanyang Technological University |
Language: | English |
Summary: | In recent years, the demand for the battery-powered devices has been increasing
rapidly. At the same time, the requirements for the audio power amplifier (APA) also
extend to hi-fi quality music playback. In order to achieve high run time per charge
for the portable devices, the quiescent power consumption of APA should be made as
low as possible. As such, the quiescent power consumption, harmonic distortion and
dynamic range become the most significant performance parameters in the design of
high-performance headphone amplifiers. Compared to the class-D amplifier, class
AB amplifier has the key advantages of high PSRR, low THD+N, no switching noise
and no electro-magnetic interference.
In this thesis, a low-quiescent class-AB headphone driver, which is powered by dual
supplies of ±1V, is presented and analyzed. Due to the small resistive load of APA,
the mismatch-induced quiescent current caused by the input-referred offset voltage
becomes a significant effect on the quiescent power consumption. It is evident that
the mismatch-induced quiescent current of APA will be substantially increased with
the increase of amplifier offset. A new balanced offset compensation current
approach is presented. Through the aid of digitally-assisted calibration design, the
input-referred offset can be substantially reduced while avoiding the unnecessary
increase of quiescent power. Since the compensation current is injected into the low
impedance nodes of the front-end gain stage, there is no significant degradation in
terms of DC gain and power supply rejection ratio (PSRR) of the amplifier. This has
demonstrated the robustness of calibration circuit.
An improved compensation technique called NMCFNR2, which is the Type-II
implementation of nested Miller compensation with feedforward and nulling resistor
(NMCFNR) amplifier, is proposed. It offers the technical advantages of simplicity as
well as low-quiescent operation. Besides, the modified frequency compensation
permits the APA to drive the worst-case load of 16Ω//2nF whilst sustaining good
stability and offering good and balanced performance metrics.
Together with the channel-length modulation (CLM) reduced class-AB bias
generation circuit dedicated to the push-pull output stage, the auto-calibrated APA
will reduce the input-referred offset of amplifier down to about 85µV while the total
quiescent power is only 0.4mW and the GBW is of about 1.78 MHz. The APA can
deliver a peak power of 35mW (1.5Vpp swing) to the worse case load of (16Ω//2nF)
with -89dB THD+N and 93.5dB SNR. The extensive measurement results have
suggested that the proposed amplifier has achieved the best Figure-of-Merit FOM1=
(Peak load power/Quiescent power) and the best FOM2= [Peak load
power/Quiescent power*(THD+N)%] when compared with other representative
state-of-the-art works. |
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