Apparatus and method for frequency calibration between two radios

• US 7,746,922 B2
• Filed: 12/07/2005
• Issued: 06/29/2010
• 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 R., Wright, David
• Primary Examiner(s): Ahn, Sam K
• Application Number:
  US11/297,505
• Publication Number:
  US 20070127562A1
• Time in Patent Office: 1,665 Days
• Field of Search: 375224-228, 370/516, 370/247, 370/251, 702/69, 702/120, 702/121, 348/497, 324/513, 324/523, 324/527, 324/528, 324/750, 324/755, 324/763, 324/765, 379/21, 379/26.02, 379/27.04, 700/39, 700/81, 714/30, 714/36, 714/715, 714/734, 714/738
• US Class Current: 375/226
• 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 configured to generate a reference frequency;

a radio circuit configured to operate according to the reference frequency; and

a frequency offset circuit configured to generate, based on signal quality information in a wireless data signal received from a second wireless device, an offset value to reduce an operating frequency offset between the wireless device and the second wireless device, wherein the frequency offset circuit comprises an accumulator circuit, and wherein an overflow rate of the accumulator circuit represents the operating frequency offset of the radio circuit.

2. The wireless device of claim 1, wherein the frequency offset circuit is configured to:

adjust an operating frequency of the radio circuit in a first direction and measure a signal reception quality;

repeatedly adjust the operating frequency of the radio circuit further in the first direction when a re-measured signal reception quality improves; and

adjust the operating frequency in a second direction generally opposite to the first direction when the re-measured signal reception quality gets worse.

3. The wireless device of claim 1, wherein the accumulator circuit is configured to receive an instantaneous frequency of a Radio Frequency (RF) signal at a first input, a programmable constant at a second input, and includes an accumulator circuit output.

4. The wireless device of claim 3, wherein the frequency offset circuit comprises a digital filter configured to sample the reference frequency and output the instantaneous frequency of the RF signal.

5. The wireless device of claim 1, wherein the signal quality information comprises an indicator of the operating frequency offset between the wireless device and the second wireless device.

6. The wireless device of claim 5, wherein the indicator of the operating frequency offset comprises one or more of:

a Bit Error Rate (BER), packet error rate, or a signal strength.

7. The wireless device according to claim 1, wherein the wireless radio circuit is a two-way transceiver.

8. A frequency calibration method comprising:

adjusting a first operating transmit frequency on a transmitting device to establish an operating transmission frequency range for wireless data transmissions between the transmitting device and a receiving device; and

based on the operating transmission frequency range, generating a second operating transmit frequency for the wireless data transmissions by inputting to an accumulator, a signal representing an instantaneous frequency of the first operating transmit frequency and adjusting an overflow rate from the accumulator to obtain the second operating transmit frequency, wherein the second operating transmit frequency is associated with a reduced amount of carrier-based operating frequency offset between the transmitting device and the receiving device.

9. The method of claim 8, wherein a reference frequency offset between the transmitting and receiving devices is measured in the receiving device.

10. The method of claim 8, wherein the adjusting comprises:

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

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

11. The method of claim 10, wherein the second operating transmit frequency comprises a frequency value centered between the first offset transmit frequency and the second offset transmit frequency.

12. The method of claim 8, wherein an amount of corruption associated with individual wireless data transmissions is determined by measuring at least one of:

a received signal strength of an RF transmission or a Bit Error Rate (BER).

13. The method of claim 12, further comprising:

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

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

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

14. The method of claim 8, wherein the adjusting the first operating transmit frequency and the generating the second operating transmit frequency is initiated in response to reception of data transmissions with a high Bit Error Rate (BER).

15. The method of claim 8, wherein the adjusting the first operating transmit frequency and the generating the second operating transmit frequency is initiated in response to a change in temperature measured at the transmitting device or the receiving device.

16. 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;

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

a frequency offset circuit configured to generate an offset carrier-based operating frequency of the radio transmitter according to the calculated signal integrity, wherein the frequency offset circuit comprises an accumulator circuit, and wherein an overflow rate of the accumulator circuit represents the offset carrier-based operating frequency of the radio transmitter.

17. The radio system of claim 16, wherein the processing element is configured to determine the signal integrity according to a Bit Error Rate (BER) for the radio transmission.

18. The radio system of claim 17, wherein the frequency offset circuit is configured to repeatedly generate the offset carrier-based operating frequency in response to the BER until the BER value is within a desired range.

19. The radio system of claim 16, wherein the accumulator circuit is configured to receive a signal at an instantaneous frequency of the transmitter crystal oscillator at a first input, a programmable constant at a second input, and includes an accumulator circuit output.