Distributed decimation sample rate conversion

• US 5,880,980 A
• Filed: 09/30/1996
• Issued: 03/09/1999
• Est. Priority Date: 09/30/1996
• Status: Expired due to Term

• Current Assignee: Conexant Systems Incorporated (Synaptics Incorporated)
• Original Assignee: Rockwell International Corporation
• Inventors: Shamlou, Daryush, Rothacher, Fritz M.
• Primary Examiner(s): NGO, CHUONG D
• Application Number:
  US08/724,168
• Time in Patent Office: 890 Days
• Field of Search: 364/723, 364/724.1, 341/143, 341/155, 341/157
• US Class Current: 708/313
• CPC Class Codes: G06T 3/4023 based on decimating pixels or lines of pixels; based on inserting pixels or lines of pixels
• CPC Class Codes: H03H 17/0642 the ratio being arbitrary or irrational
• CPC Class Codes: H03H 17/0685 the ratio being rational

Abstract

A system for decimating a source signal with a source sample rate by a non-integer factor to a sink signal with a sink sample rate is disclosed. The system first determines a decimation factor based on a ratio of the source sample rate to the sink sample rate. The system then decimates the source signal by the decimation factor to an intermediate ("IM") signal with an IM sample rate which is larger than the sink sample rate. The IM signal is then applied to a sample-rate converter to down convert to the sink signal with the sink sample rate, using a decimation factor between only 1 and 2.

Claims

1. A method of decimating a source signal with a source sample rate by a non-integer ratio to a sink signal with a sink sample rate, comprising the steps of:

a) determining a largest power-of-2 decimation factor based on the source sample rate and the sink sample rate;

b) decimating the source signal by the decimation factor to an intermediate signal with an intermediate ("IM") sample rate which is as least as large as the sink sample rate;

c) applying sample-rate conversion to the IM signal to down convert to the sink signal with the sink sample rate.

2. A method according to claim 1, wherein the IM signal has a sample rate between about 1×

and about 2×

of the sink sample rate.

3. A method according to claim 2, wherein the step c) applies the sample rate conversion with a down-conversion factor between 1 and 2, inclusive.

4. A method of decimating a source signal with a source sample rate to a sink signal with a sink sample rate, comprising the steps of:

a) determining ratio of the source sample rate to the sink sample rate;

b) determining a power-of-2 decimation factor based on the ratio;

c) decimating the source signal by the decimation factor to an IM signal with an IM sample rate, where the IM sample rate is larger than the sink sample rate;

d) converting the IM signal by a non-integer factor to the sink signal with the sink sample rate by using a sample rate converter.

5. The method according to claim 4, wherein the IM sample rate is between about 1×

and about 2×

the sink sample rate.

6. The method according to claim 5, wherein the source signal is an oversampled signal of an input signal.

7. A system for decimating a source signal with a source sample rate by a non-integer ratio to a sink signal with a sink sample rate, comprising:

means for determining a power-of-2 decimation factor based on a ratio of the source sample rate to the sink sample rate;

variable decimation filter means for decimating the source signal by the decimation factor to an intermediate signal ("IM") with an IM sample rate which is larger than, or equal to, the sink sample rate, the variable decimation filter means comprising a SINC filter;

sample-rate converter means for down-converting the IM signal by a non-integer factor to the sink signal with the sink sample rate.

8. The system according to claim 7, wherein the variable decimation filter means decimates the source signal to the IM signal with a sample rate between about 1×

and about 2×

of the sink sample rate, using a programmable decimator factor.

9. The system according to claim 8, wherein the sample-rate converter means converts using a conversion factor between 1 and 2.

10. The system according to claim 9, wherein the source signal is oversampled by an oversampling factor, wherein the variable decimation filter means comprises:

variable decimation integrator mean for integrating and decimating the source signal to generate an integration output, using one of the following decimation factors;

32, 64, 128, and 256 based on the oversampling factor and the sink sample rate;

differentiator means coupled to the integrator means for differentiating the integration output to generate a differentiator output;

FIR droop correction means coupled to the differentiator means for correcting high-frequency attenuation from the SINC filter to generate a corrected output;

first FIR halfband filter means coupled to the FIR droop correction means for down-converting the corrected output by a factor of 2;

second FIR halfband filter means coupled to the first FIR halfband filter means for generating the IM signal with the IM sample rate by a factor of 2.