Low Voltage Analog Baseband for WiMAX
Date Issued
2006
Date
2006
Author(s)
Kao, Tze-Huei
DOI
en-US
Abstract
As continuous improvement in the integrated circuit process, the gate-oxide breakdown voltage is declining due to the shrinking gate length of MOS-transistors. To go with the trend of descending supply voltage, this thesis is focused on the implementation of low voltage operation analog baseband circuits for WiMAX direct-conversion receivers. The realized chips in this work can be generally divided into three categories according to their operation voltages, namely 1.0-V, 1.8-V and 0.5-V.
The 1.0-V analog baseband circuit was implemented with low threshold voltage devices provided by standard process while adopting the active–RC topology to achieve low-pass filtering. The 7th order Chebyshev channel selection filter prototype is realized through the cascade method. With a merged function of variable-gain amplifier, the output signal can accommodate to the dynamic range of the following ADC. The servo loop configuration is adopted to accomplish dc-offset cancellation. The circuit exhibited a 3-dB bandwidth of 5.3 MHz, a voltage gain from 20 to 50 dB while drawing 9.9 mW from a 1.0-V voltage supply. The die area is 0.7×1.1 mm2.
The 1.8-V filter can switch to different gain levels and bandwidths to adapt to the communication standards. A successive approximation register ADC along with DAC current source array were used to achieve dc-offset cancellation. An automatic frequency tuning loop based on master-slave topology is implemented on the same chip to prevent the inaccuracy of filter bandwidth due to process and temperature variations. With this tuning loop, the precise filter bandwidth at 5.0 MHz, 10.0 MHz and 20.0 MHz can be obtained. The chip provides 20 to 60 dB gain and consumes 27.8 mW with a chip size of 1.5 × 2.0 mm2.
In contrast with the 1.0-V version, a 0.5-V filter is implemented using standard devices with normal threshold voltage. Utilizing the body-biasing technique and adopting a structure with the fewest stacks of transistors enable the op-amp to operate under ultra low voltage comparable with device threshold voltage. The leapfrog structure is adopted to synthesize the 5th order Chebyshev low pass filter. While drawing 6.8 mW from a 0.5-V voltage supply, the filter demonstrated a 3-dB bandwidth of 2.6 MHz. In addition, the voltage gain can be varied from 0 to 9.8 dB through an external resistor. The die area is 1.0×1.3 mm2.
Subjects
低電壓
類比基頻電路
濾波器
low voltage
analog baseband
filter
Type
thesis
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