A simulation low-pass filter

Abstract

The present invention provides an analog low-pass filter. The digital signal which is modulated by a 3-stage 1-bit sigma-delta in the front end circuit is executed with low-pass filtering, wherein a semi-digital filtering and an analog low-pass filtering are included. The composition comprises a shifting register, a tap coefficient circuit and an output stage power amplifier circuit. The invention is characterized in that the tap coefficient circuit wherein is a tap resistance network. The output end of each shifting register is connected with the tap resistance network through a controlled current source. The controlled current source is overlapped to a filtering analog (sine) signal on each tap resistor for totalizing the filtering analogue signal and amplifying the power to obtain the final analog output signal. The shifting register is a D trigger and the controlled current source is a current steering circuit.

Description

technical field [0001] The invention relates to the technical field of signal processing, in particular to an analog DAC output circuit or an analog low-pass filter based on sigma-delta modulation. Background technique [0002] The present invention is an analog DAC output circuit of an FIR digital filter, and its main function is to perform low-pass filtering on the digital signal modulated by 3-order 1-bit sigma-delta in the pre-circuit, including half-digital filtering and analog low-pass filtering, The latter is output through a power output amplifier. In the pre-circuit of the analog DAC output circuit, the original digital signal has been compensated and filtered, interpolated and truncated into a 1-bit signal stream. The whole modulation process is to make the signal within the required frequency band. High, the noise brought by the original digital signal is modulated to the high frequency as much as possible, so that the low-pass filter in this circuit can make the...

AI Technical Summary

Problems solved by technology

In this circuit, the weighted current source is used to realize the entire filter coefficient, so the current source should be proportional to the coefficient. Since the values ​​of each coefficient are different, a large number of proportional current sources should be designed in the design, which is difficult to guarantee in terms of digital-to-analog conversion accuracy. , the current of the current source will be biased, which will affect the final filtering effect

Secondly, in the design of the low-pass filter, two amplifiers are used in the whole circuit, and an RC low-pass filter circuit is used, which will increase power consumption, especially in low-voltage and low-power consumption circuits.

At the same time, since the amplifiers are not fully differential, there will be obvious defects in performance such as anti-noise interference and power supply rejection ratio.

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