Finite Impulse Response (FIR) upsample Filters

Collaboration diagram for Finite Impulse Response (FIR) upsample Filters:

Functions
void	tpt_fir_upsample_f32 (f32_t *aOutData, const tpt_fir_upsample_f32_t *aFilter, f32_t *aInData, uint32_t aCount)
	Function for the floating-point Upsampling FIR filter. More...
void	tpt_fir_upsample_q15 (q15_t *aOutData, const tpt_fir_upsample_q15_t *aFilter, q15_t *aInData, uint32_t aCount)
	Function for the q15 Upsampling FIR filter. More...
void	tpt_fir_upsample_q31 (q31_t *aOutData, const tpt_fir_upsample_q31_t *aFilter, q31_t *aInData, uint32_t aCount)
	Function for the q31 Upsampling FIR filter. More...

Detailed Description

This functions implement the Upsampling Fir Filter by combine an FIR filter together with a upsampler. They are used in multirate systems for increasing the sample rate of a signal without introducing high frequency images.

When upsampling by a factor of L, the signal should be filtered by a lowpass filter with a normalized cutoff frequency of 1/L in order to prevent aliasing distortion. The upsampler inserts L-1 zeros between each sample.

The functions operate on blocks of input and output data. src points to an array for the length aCount values and the output dst points to an array of the length aCount * L values. The functions use a polyphase filter structure:

       dst[n] =  b[0] * src[n] + b[L]   * src[n - 1] + ...
                   + b[L * (plen - 1)] * src[n - plen + 1]
      dst[n + 1] =  b[1] * src[n] + b[L + 1]   * src[n - 1] + ...
                       + b[L * (plen - 1) + 1] * src[n - plen + 1]
           ...
       dst[n + (L - 1)] =  b[L - 1] * src[n] + b[2 * L - 1]   * src[n -
       1]
                   + ... + b[L * (plen - 1) + (L - 1)] * src[n - plen +
                   1]
       wher b[n] is the filter coefficients.
  

The coefficients and state variables for a filter are stored together in an instance data structure which is defined as follow. The state variables are updated after each block of data is processed and the coefficients are untouched.

       struct {
           uint32_t uL;
           uint32_t uLen;
           (type) *pCoeff;
           (type) *pState;
       } tpt_fir_upsample_(type)_t;

  where *pState points to the state variable array of aCount
               pLen + aCount - 1.
        *pCoeff points to the coefficient array of aCount
        uL*uPlen.
          uLen length of the polyphase filter.
             uL is the upsampling factor.
  

Function Documentation

tpt_fir_upsample_f32()

void tpt_fir_upsample_f32	(	f32_t *	aOutData,
		const tpt_fir_upsample_f32_t *	aFilter,
		f32_t *	aInData,
		uint32_t	aCount
	)

Function for the floating-point Upsampling FIR filter.

Parameters

[out]	aOutData	points to the output block data.
[in]	aFilter	points to an instance of the Upsampling FIR structure.
[in]	aInData	points to the input block data.
[in]	aCount	number of the aCount.

tpt_fir_upsample_q15()

void tpt_fir_upsample_q15	(	q15_t *	aOutData,
		const tpt_fir_upsample_q15_t *	aFilter,
		q15_t *	aInData,
		uint32_t	aCount
	)

Function for the q15 Upsampling FIR filter.

Parameters

[out]	aOutData	points to the output block data.
[in]	aFilter	points to an instance of the Upsampling FIR structure.
[in]	aInData	points to the input block data.
[in]	aCount	number of the aCount.

tpt_fir_upsample_q31()

void tpt_fir_upsample_q31	(	q31_t *	aOutData,
		const tpt_fir_upsample_q31_t *	aFilter,
		q31_t *	aInData,
		uint32_t	aCount
	)

Function for the q31 Upsampling FIR filter.

Parameters

[out]	aOutData	points to the output block data.
[in]	aFilter	points to an instance of the Upsampling FIR structure.
[in]	aInData	points to the input block data.
[in]	aCount	number of the aCount.