| Summary: | 博士 === 國立成功大學 === 電機工程學系 === 87 === In this thesis, two integrated circuits (ICs), an analog filter and a mixed-mode circuit for speech applications, using switched-current (SI) techniques are implemented. Moreover, an automatic coefficient design method of bandpass sigma-delta modulators for data converters is proposed.
The circuit specifications of the bandpass sigma-delta modulator (BPSDM) used for digital audio broadcasting (DAB) receivers are also analyzed. The analysis results will facilitate the optimization of the cost and the power consumption of BPSDMs.
In the analog filter design, this thesis proposes a new offset current cancellation technique called multiple-path
feedback compensation (MPFC) for greatly reducing offset currents at both output and internal nodes of SI circuits and systems. In order to analyze the effects and the statistical distribution of DC current offsets of large SI systems, a very simple and efficient SI model is first used. This model can be used for fast, accurate, statistical, and systematic analyses of system characteristics such as offset current, frequency response, stability, scaling, and sensitivity. Based on the model, a complex SI system can be transferred to a simple signal flow graph, which can be represented by linear state equations. From the state equations, statistical Monte-Carlo simulation is used to obtain optimal MPFC coefficients. A 5-th order Chebyshev SI filter is illustrated as an example for implementation and verification of the proposed MPFC technique. 90 test chips have been fabricated with a 1um CMOS n-well digital process. Increased percentages of circuit area and power consumption due to the use of the MPFC circuit are 5% and 4%, respectively. Measured results showthat the variance of output offset currents is reduced to 2% of its original amount. Besides, the peak signal-to-noise ratio(PSNR) is increased by 3dB and the total harmonic distortion(THD) is reduced by 10dB.
In addition, a low-cost, low-voltage, mixed-mode IC for speech applications using SI techniques is implemented in this thesis. In this design, the mixed-mode IC can directly preamplify speech signals with the aid of an automatic gain control, convert amplified signals to 1-bit digital codes with a 24Kbits/second data rate, store the converted codes in a memory, and replay the stored codes through an on-chip current-input-voltage-output power amplifier. Switched-current (SI) techniques are used to implement a filter with a 3.4KHz bandwidth and a 96KHz sampling frequency, and also an adaptive
delta modulator (ADM) with a 24KHz sampling frequency. Measured
dynamic range of the SI ADM combined with the SI filter is larger than 40dB. This mixed-mode IC, operating with a 3.3V supply voltage, was fabricated with a 1.5um single-poly-single-metal CMOS process. The whole system has been tested using real human voice and results show that it is highly suitable for low-cost speech applications.
In order to reduce the size, power consumption and cost of the wireless receiver, moving the analog-to-digital (ADC) interface closer to antenna is desirable. The bandpass sigma-delta ADC can attain these goals. This thesis is the first to realize automatic coefficients synthesis of high-order modulators used in bandpass sigma-delta ADCs. To begin with, the initial noise transfer functions (NTFs) of bandpass sigma-delta modulators (BPSDMs) are taken from inverse-Chebyshev bandreject filter functions with stopband attenuation equal to the required value. New semi-empirical stability constraints are then used to examine the initial NTFs such that only stable NTFs remain. Tradeoffs among chip area, power consumption, and
performance are made to further select a most appropriate NTF from those stable NTFs. The NTF(z) is then fitted to BPSDM structures and their corresponding coefficients can be easily obtained. Feedforward and cascade-of-resonator structures with orders of 6, 8 and 10, are used as examples in this thesis. Thus coefficients of stable BPSDMs which meet the required specifications can be automatically generated by a computer program implemented in accordance with the synthesis method. The synthesis result shows the structure coefficient spread is large while using feedforward and cascade-of-resonator structures to fit the stable NTFs. Therefore, new BPSDM structures are proposed to reduce the coefficient spread, and their low sensitivities to component variations are also shown.
A future broadcasting system named as DAB has been developed in the Europe. In this thesis, the block specifications of DAB receiver are discussed, and four BPSDM
structures which fit the system requirement are designed. Their
circuit specifications are analyzed, moreover, their differences
due to nonideal circuit effects, such as operational amplifier(OPAMP) DC finite gain, OPAMP gain nonlinearity, OPAMP
slew rate, OPAMP bandwidth, capacitor nonlinearity, and noise
budget in each resonator, are discussed and compared.
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