Low precision finite impulse response filter for digital interpolation

A digital-to-analog converter comprising:

• an input for receiving a digital input sequence at a first sampling rate;
• a sample rate converter for increasing the first sampling rate to a second and higher sampling rate;
• an interpolation filter for filtering out the images of the output of said sample rate converter, said interpolation filter having a frequency response with a pass band for passing through with minimum attenuation the converted input sequence, a stop band for attenuating the images of the converted input sequence to a predetermined level, and a transition band between the pass band and the stop band, said interpolation filter including a Finite Impulse Response (FIR) filter having low precision FIR filter coefficients associated therewith that provide a frequency response below a point in the stop band that is commensurate with substantially higher precision FIR coefficients, and which frequency response above said point in the stop band degrades in a substantially gradual manner;
• a digital-analog-converter for converting the output of said interpolation filter to an analog signal;
• and
• a low pass filter for attenuating the output of said sample rate converter above said point in the stop band.

A method for interpolating digital data, comprising the steps of:

• receiving a digital input sequence at a first sampling rate;
• converting the input first sampling rate up to a second and higher sampling rate;
• and
• filtering out the images of the converted data at the second sampling rate, and the step of filtering operating with a frequency response having a pass band for passing through with minimum attenuation the converted input data at the second sampling rate, a stop band for attenuating the images of the converted data to a predetermined level, and a transition band between the pass band and the stop band, the step of filtering including the steps of:
• providing a Finite Impulse Response (FIR) filter having low precision FIR filter coefficients associated therewith that provide a frequency response below a point in the stop band that is commensurate with substantially higher precision FIR filter coefficients, and which frequency response above the point degrades in a substantially gradual manner,
• processing the converted data at the second sampling rate through the FIR filter,
• low pass filtering the output of the FIR filter to attenuate signals above the point.

A method for converting digital signals to analog signals, comprising the steps of:

• receiving a digital input sequence at a first sampling rate;
• converting the input sequence from the first sampling rate to a second and higher sampling rate;
• filtering out the images of the converted input sequence at the second sampling rate, the step of filtering operating with a frequency response having a pass band for passing through with minimum attenuation the converted sequence, a stop band for attenuating the images of the converted sequence to a predetermined level, and a transition band between the pass band and the stop band, the step of filtering including:
• providing a Finite Impulse Response (FIR) filter having low precision FIR filter coefficients associated therewith that provide a frequency response below a point in the stop band that is commensurate with substantially higher precision FIR coefficients, and which frequency response above the point degrades in a substantially gradual manner, and
• processing the converted sequence through the FIR filter;
• processing the output of the FIR filter through a digital-to-analog converter;
• and
• low pass filtering the output of the digital-to-analog converter to attenuate signals above the point in the frequency response of the finite impulse response filter.