Apparatus and method for frequency calibration between two radios

• US 20070127562A1
• Filed: 12/07/2005
• Published: 06/07/2007
• Est. Priority Date: 12/07/2005
• Status: Active Grant

• Current Assignee: Cypress Semiconductor Corporation (Infineon Technologies AG)
• Original Assignee: Cypress Semiconductor Corporation (Infineon Technologies AG)
• Inventors: Gehring, Mark, Wright, David
• Granted Patent: US 7,746,922 B2
• Time in Patent Office: Days
• US Class Current: 375/227
• CPC Class Codes: H04B 17/318 Received signal strength
• CPC Class Codes: H04L 1/16 in which the return channel carries supervisory signals, e.g. repetition request signals
• CPC Class Codes: H04L 1/203 Details of error rate determination, e.g. BER, FER or WER
• CPC Class Codes: H04L 2027/0016 Stabilisation of local oscillators
• CPC Class Codes: H04L 2027/002 using feedback from a remote receiver
• CPC Class Codes: H04L 2027/0034 using hypothesis testing

Abstract

Wireless devices transmit and receive radio signals based upon reference frequencies generated by crystal oscillators. If the reference frequencies of the transmitter and the receiver are different, the radio signals may not be received properly or may not be received at all. A measurement circuit measures the amount of error or signal corruption in the radio signals due to the reference frequency offset between the transmitter and the receiver. A frequency offset circuit generates an offset operating frequency in the transmitter or the receiver to align or calibrate the operating frequencies of the devices.

Claims

1. A wireless device, comprising:

a crystal oscillator generating a reference frequency;

a radio circuit operating according to the reference frequency; and

a frequency offset circuit generating an offset operating frequency of the radio circuit according to a signal reception quality of a wireless data signal either transmitted or received by the radio circuit.

2. The wireless device of claim 1, wherein the frequency offset circuit offsets the operating frequency in a first direction and measures the signal reception quality, the frequency offset circuit repeatedly offsetting the operating frequency of the radio circuit further in the first direction when a re-measured signal reception quality improves and offsetting the operating frequency in a second opposite direction when the re-measured signal reception quality gets worse.

3. The wireless device of claim 1, wherein the frequency offset circuit comprises an accumulator circuit, an overflow rate of the accumulator circuit representing the offset operating frequency of the radio circuit.

4. The wireless device of claim 1, wherein the frequency offset circuit comprises an accumulator circuit receiving an instantaneous frequency of a Radio Frequency (RF) signal at a first input, a programmable constant at a second input, and an output of the accumulator circuit at a third input.

5. The wireless device of claim 4, wherein the frequency offset circuit comprises a digital filter having an input connected to sample the reference frequency and outputting the instantaneous frequency of the RF signal.

6. The wireless device of claim 1, wherein the frequency offset circuit generates the offset operating frequency according to a Bit Error Rate (BER) of the wireless data signal.

7. The wireless device of claim 1, wherein the frequency offset circuit generates the offset operating frequency according to a received signal strength of the wireless data signal.

8. The wireless device according to claim 1 wherein the wireless radio circuit is a two-way transceiver that offsets an operating transmit frequency according to reception quality information transmitted back from a radio receiver.

9. A method of calibrating frequencies between radios, comprising:

determining an amount of corruption in a data transmission at an operating frequency due to reference frequency offset between transmitting and receiving devices used in the data transmission; and

generating an offset operating frequency for one of the transmitting and receiving devices to reduce the amount of operating frequency offset between the devices.

10. The method of claim 9, wherein the reference frequency offset between the transmitting and receiving devices is measured in the receiving device.

11. The method of claim 9, wherein generating the offset operating frequency comprises:

generating a first offset transmit frequency by adjusting the operating frequency back and forth from one direction to an opposite direction until the amount of corruption measured by a Bit Error Rate (BER) is low;

generating a second offset transmit frequency by adjusting the first offset transmit frequency back and forth from one direction to an opposite direction until the amount of corruption measured by the BER is high; and

generating the offset operating frequency according to a frequency value centered between the first offset transmit frequency and the second offset transmit frequency.

12. The method of claim 9, wherein the amount of corruption is determined by measuring a Bit Error Rate (BER) in the data transmission.

13. The method of claim 9, wherein the amount of corruption is determined by measuring a received signal strength of an RF transmission.

14. The method of claim 9, comprising:

repeatedly determining an amount of operating frequency offset between the transmitting and receiving devices;

repeatedly offsetting the operating frequency of one of the transmitting and receiving devices according to the amount of operating frequency offset; and

repeatedly recalculating an amount of corruption in a next data transmission using the offsetted operating frequency.

15. The method of claim 9, wherein offsetting the operating frequency is initiated in response to reception of data transmissions with a high Bit Error Rate (BER).

16. The according of claim 9, wherein offsetting the operating frequency is initiated in response to a change in temperature measured at either the transmitting or receiving devices.

17. A radio system, comprising:

a radio transmitter configured to transmit a radio transmission according to a transmitter crystal oscillator frequency;

a radio receiver configured to receive and process the radio transmission according to a receiver crystal oscillator frequency; and

a processing element configured to calculate a signal integrity for the received radio transmission; and

a frequency offset circuit configured to generate an offset operating frequency according to the calculated signal integrity.

18. The radio system of claim 17, wherein the processing element determines the signal integrity according to a Bit Error Rate (BER) for the radio transmission.

19. The radio system of claim 18, wherein the frequency offset circuit repeatedly generates the offset operating frequency in response to the BER until the BER value is within a desired range.

20. The radio system of claim 17, wherein the processing element determines the signal integrity according to a received signal strength of the received radio transmission.