Method and apparatus employing decimation filter for down conversion in a receiver

• US 6,373,422 B1
• Filed: 10/26/2000
• Issued: 04/16/2002
• Est. Priority Date: 10/26/2000
• Status: Active Grant

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Mostafa, Mohamed A.
• Primary Examiner(s): YOUNG, BRIAN K
• Application Number:
  US09/697,190
• Time in Patent Office: 537 Days
• Field of Search: 341/155, 341/126, 341/156, 341/165, 341/172
• US Class Current: 341/155
• CPC Class Codes: H04B 1/30 for homodyne or synchrodyne receivers demodulator circuits H03D1/22

Abstract

A radio frequency receiver includes a mixer (508) for converting a radio frequency signal into an IF signal. The IF signal is then filtered and amplified by a filter (510) and automatic gain control circuit (512). The filtered and amplified IF signal is then received by an analog-to-digital converter (514) in order to convert the signal from an analog signal into a digital signal. The digital signal is then provided to a decimation filter (516) in order to convert the digital signal into a base band signal (520). The ADC (514) and decimation filter (516) both are provided with a sampling frequency signal (518) which is preferably at least four times greater than the IF signal. By using a decimation filter (516) the need for a second down conversion mixer is eliminated, thereby eliminating any associated noise, power consumption and distortion associated with using a second mixer.

Claims

1. A radio frequency receiver, comprising:

a mixer for receiving a radio frequency signal and a local oscillator signal and providing an output intermediate frequency (IF) signal;

an analog-to-digital converter (ADC) for receiving the IF signal and converting it into a digital signal;

a decimation filter responsive to the digital signal; and

the ADC and decimation filter receive a sampling frequency signal (Fsample) which is a multiple factor of the IF frequency signal, and the decimation filter converts the digital signal provided by the ADC to a base band signal.

2. A radio frequency receiver as defined in claim 1, wherein the sampling frequency signal is four times greater than the IF.

3. A radio frequency receiver as defined in claim 1, wherein the decimation filter uses a decimation factor equal to the multiple factor or a multiple of the multiple factor.

4. A radio frequency receiver as defined in claim 3 wherein the multiple factor is equal to four.

5. A method for demodulating an RF signal, comprising the steps of:

mixing the RF signal with a local oscillator signal and providing an intermediate frequency (IF) signal;

converting the IF signal into a digital signal using an analog-to-digital converter (ADC); and

decimating the digital signal using a decimation filter in order to produce a baseband signal.

6. A method as defined in claim 5, wherein the ADC and the decimation filter are provided a sampling frequency equal to the IF signal frequency times a multiple factor.

7. A method as defined in claim 6, wherein the multiple factor is equal to four.

8. A method as defined in claim 7, wherein the decimation filter uses a decimation factor equal to four.

9. A method as defined in claim 7, wherein the decimation filter uses a decimation factor equal to four or a multiple of four.

10. A method as defined in claim 6, wherein the decimation filter uses a decimation factor equal to the multiple factor or a multiple of the multiple factor.