This paper describes a new first-and second-order delta-sigma modulator concept where the first integrator is extracted and implemented by a frequency modulator with the modulating signal as the input. The result is a simple delta-sigma modulator with no need for digital-to-analog converters, allowing straightforward multi-bit quantization. Without the frequency modulator, the circuit becomes a frequency-to-digital converter with delta-sigma noise shaping. An experimental first-and second-order modulator have been implemented in a 1.2-¼m standard digital CMOS process and the results confirm the theory. For the first-order modulator an input signal amplitude of 150mV resulted in a SQNR of ³115dB at 2MHz sampling frequency and signal bandwidth 500Hz.
The development of transmission networks and magnetic components for the L5 system represents the largest network development project of its type ever undertaken within the Bell System. Over 200 different coded designs of networks, requiring in excess of 40 man‐years of effort, were required to meet the frequency‐selective and signal‐shaping requirements of the system. Despite this effort, neither systems requirements nor systems schedules could have been met without significant contributions from allied technologies. This article identifies those technologies and describes design techniques that have advanced the state‐of‐the‐art capabilities in transmission network and magnetic component design.
This paper describes a new first and secalndorder delta-sigma modulator (DSM) concept where the first integrator is extracted and implemented by a FM osciilator with the modulating signal as the input. The resullt is a simple DSM with no need for DACs, :allowing straightforward multi-bit quantization. Without the FM oscillator, the modulator becomes a F/D converter with delta-sigma noise shaping. I. I N T R O D U C T I O NThe delta-sigma (A-E) A/D conversion technique [ 11 is (currently receiving increased attention as an attractive alternative to traditional A/D conversion. Although the :DSM is well suited for VLSI implementation, multi-bit quantization is not straightforward due to DAC limitations, and the sampling speed is limited by the integrator slew-rate.By implementing the main integrator as a FM oscil1,ator we achieve a simpler modulator without D.ACs, and straightforward multi-bit quantization and higher sampling frequency potential is one amongst other features. The new DSM that .will be referred to as a frequency DSM (FDSM) imay become a :F/D converter with A-C noise shaping just by removing the FM oscillator. Compared to the ACFDC in [2] the FDSM concept is simpler, and as opposed to the second-orcler architecture reported in [3] the FDSM offers multi-bit quantization.To illustrate why a FM oscillator may be u:;ed as an integrator we may look at the FM signal itself. An idcal logic level FM signal may be expressed as(2) s:, In this expression fc represents the carrier firequency, x (z) the modulating signal, and k the frequency sensitivity. From (2) we see that the FM signal variable B(t)/2n. is the integral of fc + k x ( t ) . The equation B(t)/2n may be separated into Qn /2j7 = Pn + @n 9(3 )where Pn is an integer representing the received number of rising FM edges at time n T r , and @n E [O, 1) is the phase difference between the previous rising FM edge and the sample signal edge scaled by 1/2n. Figure 1 : A. first-order FDSM T H E F I R S T O R D E R FDSMA very simple DSM implementation is made by replacing the single loop integrator of a first-order DSM with a FM oscillator. By doing so, we have got an integrator with a high S N R potential that never saturates, so the feedback may be removed.For integer quantization thresholds, the resulting FDSM may be implemented by the circuit illustrated in Fig. 1. The output is merely the number of received FM periods P,, -P,,-during the sampling interval T, = 1/ fs. By replacing P,, with e, , f 271. -& (3), and from (2) representing Qn/2n as T, C:=-,(fc + k x i ) , the output may be written as (4) By considering the modulating signal x,, as the input, we have a first-order DSM where the input is scaled and biased, and the quantization error +, , is differentiated. Although we are using a FM intermediate value, the circuit implement first-order A-Z A/D conversion.If the signal source itself contains a FM oscillator, we have shown that for F/D conversion or digital FM demodulation, we achieve equivalent first-order A-X noise shaping with respect to the modu...
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