Radio frequency (RF) receiver with amplitude-shifted keying/frequency-shifted keying (ASK/FSK) duty cycle optimization algorithm

1. A method of operating a radio frequency (RF) receiver for an automobile comprising the steps of:

operating the RF receiver in a first mode for receiving Frequency Shift Keyed (FSK) modulated transmissions for a first period;

switching the RF receiver to a second mode for receiving an Amplitude Shift Keyed (ASK) modulated transmission for a second period, shorter than the first period;

switching the RF receiver back to the first mode responsive to the RF receiver determining that an ASK modulated transmissions is present;

switching the RF receiver back to the second mode after a first known time interval such that the RF receiver can receive a second ASK modulated transmission; and

maintaining the RF receiver in the second mode after the first known time interval to received the second ASK modulated transmission.

2. The method as recited in claim 1 , wherein the second period is of a duration determined to detect the presence of the first ASK modulated transmission and shorter than a period required to receive the entire first ASK modulated transmission, such that receipt of the first ASK modulated transmission in the second period provides a prompt for the RF receiver to operate in the second mode to receive a second ASK modulated transmission.

3. The method as recited in claim 2 , wherein a first time interval between the first ASK modulated transmission and the second ASK modulated transmission is fixed.

4. The method as recited in claim 3 , wherein the first period is of a duration shorter than the first time interval between the first ASK modulated transmission and the second ASK modulated transmission.

5. The method as recited in claim 1 , wherein a second time interval between receiving a first FSK modulated transmission and a second FSK modulated transmission is variable.

6. The method as recited in claim 1 , wherein the ASK modulated transmission is transmitted for a remote keyless entry (RKE) system and includes several identical packets of data transmitted at fixed intervals.

7. The method as recited in claim 1 , wherein the FSK modulated transmission is transmitted for a tire pressure monitoring (TPM) system and includes several identical packets of data transmitted at variable intervals.

8. The method as recited in claim 7 , wherein the variable intervals between the several data packets varies responsive to detected operating condition of the automobile.

9. A method of operating an RF receiver for an automobile comprising the steps of:

a) operating the RF receiver in a first mode for receiving Frequency Shift Keyed (FSK) modulated transmissions for a first period:

b) switching the RF receiver to a second mode for receiving an Amplitude Shift Keyed (ASK) modulated transmission for a second period, shorter than the first period, wherein the second period is of a duration determined to detect the presence of the first ASK modulated transmission and shorter than a period required to receive the entire first ASK modulated transmission such that receipt of the first ASK modulated transmission in the second period provides a prompt for the RF receiver to operate in the second mode to receive a second ASK modulated transmission;

c) switching the RF receiver back to the first mode responsive to the RF receiver determining that no ASK modulated transmissions is present; and

d) maintaining the RF receiver in the second mode responsive to a first ASK modulated transmission being detected, wherein a first time interval between the first ASK modulated transmission and the second ASK modulated transmission is fixed and RF receiver switches back to operate in the first mode responsive to receiving the first ASK modulated signal until the first time interval expires where the RF receiver switches back to the second mode to receives the second ASK Modulated signal.

10. A method of receiving transmissions from a tire pressure monitoring (TPM) system and a remote keyless entry (RKE) system with one RF receiver comprising the steps of:

operating the RF receiver in a first mode for receiving a Frequency Shift Keyed (FSK) modulated transmission from the TPM system for a first period;

switching the RF receiver to a second mode for receiving an Amplitude Shift Keyed (ASK) modulated transmission from the RKE system for a second period shorter than the first period and shorter than the ASK modulated transmission;

searching for an ASK modulated transmission; and

switching the RF receiver back to the first mode responsive to no ASK modulated transmission being detected, and prompting the RF receiver to switch into the second mode after a first known time interval for receiving a second ASK modulated signal responsive to receiving a first ASK modulated transmission during the second period.

11. The method as recited in claim 10 , including the step of determining the time at which the second ASK transmission is expected responsive to receiving the first ASK transmission.

12. The method as recited in claim 11 , wherein a first interval between the first ASK transmission and the second ASK transmission is fixed.

13. The method as recited in claim 10 , wherein a second interval between a first FSK modulated transmission and a second FSK modulated transmission is variable.

14. The method as recited in claim 10 , wherein the second period is shorter than the first period and shorter than a duration of the first and second ASK modulated transmissions.