1. A method for freeze protection for a temperature control system, the temperature control system for controlling the temperature of a temperature-controlled space at a set point temperature, the method comprising:
monitoring a discharge air temperature;
monitoring a return air temperature;
setting a target temperature to equal the set point temperature;
controlling the return air temperature at the target temperature; and
adjusting the target temperature based on the return air temperature when the discharge air temperature drops to one of at or below freezing.
2. The method of claim 1, wherein controlling the return air temperature includes cooling the refrigerated space in a cool mode and heating the refrigerated space in a heat mode, the method further comprising:
setting a timer to count the duration of the cool mode; and
lowering the target temperature when the timer reaches a predetermined time.
3. The method of claim 2, further comprising lowering the target temperature by one degree when the timer reaches ten minutes.
4. The method of claim 2, wherein lowering the target temperature includes lowering the target temperature when the timer reaches the predetermined time without the discharge air temperature dropping to one of at or below freezing.
5. The method of claim 2, further comprising incrementing a transition counter when the temperature control system switches between the cool mode and the heat mode.
6. The method of claim 5, further comprising lowering the target temperature when the transition counter reaches a predetermined count.
7. The method of claim 6, further comprising lowering the target temperature by one degree when the transition counter equals 5.
8. The method of claim 6, wherein the timer is a first timer and the predetermined time is a first predetermined time, the method further comprising:
setting a second timer to count the duration of the heat mode; and
lowering the target temperature when the second timer reaches a second predetermined time.
9. The method of claim 8, further comprising lowering the target temperature by one degree when the second timer reaches ten minutes.
10. The method of claim 2, wherein the timer is a first timer and the predetermined time is a first predetermined time, the method further comprising:
setting a second timer to count the duration of the heat mode; and
lowering the target temperature when the second timer reaches a second predetermined time.
11. The method of claim 1, wherein controlling the return air temperature includes cooling the refrigerated space in a cool mode and heating the refrigerated space in a heat mode, the method further comprising:
incrementing a transition counter when the temperature control system switches between the cool mode and the heat mode.
12. The method of claim 11, further comprising lowering the target temperature by one degree when the transition counter equals 5.
13. The method of claim 1, further comprising determining whether the set point temperature is in the fresh temperature range.
14. A temperature control system for controlling the temperature of a temperature-controlled space at a set point temperature, the temperature control system comprising:
a heat exchange assembly for heating the refrigerated space in a heat mode and cooling the refrigerated space in a cool mode, the heat exchange assembly positioned in communication with air in the refrigerated space by way of a return air flow path and a discharge air flow path;
a return air temperature sensor positioned in the return air flow path for sensing a return air temperature;
a discharge air temperature sensor positioned in the discharge air flow path for sensing a discharge air temperature;
a controller for controlling the return air temperature to a target temperature, the controller being programmed to adjust the target temperature based on the return air temperature sensed by the return air temperature sensor when the discharge air temperature drops to one of at or below freezing.
15. The temperature control system of claim 14, further comprising a cool mode timer for counting the duration of the cool mode, wherein the controller is programmed to lower the target temperature when the timer reaches a predetermined time without the discharge air dropping to one of at or below freezing.
16. The temperature control system of claim 15, wherein the controller is programmed to lower the target temperature by one degree when the timer reaches ten minutes.
17. The temperature control system of claim 15, further comprising a transition counter for counting the number of times the temperature control system switches between the cool mode and the heat mode, wherein the controller is programmed to lower the target temperature when the transition counter reaches a predetermined count without the discharge air dropping to one of at or below freezing.
18. The temperature control system of claim 17, wherein the controller is programmed to lower the target temperature by one degree when the transition counter equals 5.
19. The temperature control system of claim 17, further comprising a heat mode timer for counting a duration of the heat mode, wherein the controller is programmed to lower the target temperature when the heat mode timer reaches a predetermined time without the discharge air dropping to one of at or below freezing.
20. The temperature control system of claim 19, wherein the controller is programmed to lower the target temperature by one degree when the heat mode timer reaches ten minutes.
21. The temperature control system of claim 14, further comprising a heat mode timer for counting a duration of the heat mode, wherein the controller is programmed to lower the target temperature when the heat mode timer reaches a predetermined time without the discharge air dropping to one of at or below freezing.
22. The temperature control system of claim 14, further comprising a transition counter for counting the number of times the temperature control system switches between the cool mode and the heat mode, wherein the controller is programmed to lower the target temperature when the transition counter reaches a predetermined count without the discharge air dropping to one of at or below freezing.
23. A method for freeze protection for a temperature control system, the temperature control system for controlling the temperature of a temperature-controlled space at a set point temperature, the method comprising:
monitoring a discharge air temperature;
monitoring a return air temperature;
setting a target temperature to equal the set point temperature;
controlling the return air temperature at the target temperature, including
cooling the refrigerated space in a cool mode, and
heating the refrigerated space in a heat mode; and
adjusting the target temperature based on the return air temperature when the discharge air temperature drops to one of at or below freezing, including
setting a timer to count the duration of the cool mode and lowering the target temperature when the timer reaches a predetermined time, and
incrementing a transition counter when the temperature control system switches between the cool mode and the heat mode and lowering the target temperature when the transition counter reaches a predetermined count.
The claims below are in addition to those above.
All refrences to claim(s) which appear below refer to the numbering after this setence.
1. Apparatus for calibration of a phase-locked loop including a frequency divider, the apparatus comprising:
logic to automatically calibrate an integration filter of the phase-locked loop based on a predefined filter transfer function, wherein said calibration is independent of the frequency divider parameters and the integration filed is calibrated by setting the value of one or more components of the integration filter to achieve a desired RC product set to achieve a predefined RC time constant, wherein the components include a resistive component and a capacitive component and the resistive component is set to achieve the desired RC product based on the value of the capacitive component, and wherein the logic to automatically calibrate an integration filter includes:
a plurality of resistive elements;
a plurality of switches configured to couple ones of the plurality of resistive elements to a charging current circuit;
a first transistor coupled to a first of the plurality of resistive elements;
an amplifier circuit coupled to the first transistor, said amplifier circuit configured to fix a charging current based on a reference voltage; and
logic to automatically calibrate a charge pump current of the phase-locked loop, wherein the integration filter and charge pump current are calibrated to achieve a desired phase-locked loop performance level.
2. The apparatus of claim 1 wherein the plurality of switches are controlled by a switching circuit configured to adjust said plurality of switches responsive to the predefined RC time constant.
3. The apparatus of claim 2 wherein the logic to automatically calibrate an integration filter further comprises:
a current mirror circuit coupled to the first transistor; and
a comparator coupled to the current mirror; said comparator configured to receive a reference voltage and a capacitance voltage and provide an output signal to the switching circuit.
4. A method for precision calibration of a phase locked loop comprising the steps of:
automatically calibrating the pole and zero locations of a phase locked loop integration filter to a desired transfer function; and
automatically calibrating the charge pump current of a charge pump circuit based at least in part on the calibrated pole and zero location parameters, wherein said charge pump calibration is based on a desired transfer function; wherein said automatically calibrating the pole and zero locations of a phase locked loop integration filter to a desired transfer function comprises:
setting a variable resistive element of the integration filter to a first value;
comparing an RC time constant of the variable resistive element and a capacitive element to a reference time constant; and
adjusting the value of the variable resistive element responsive to said comparing.
5. The method of claim 4 further comprising repeating said comparing and adjusting if the value of the RC time constant does not match the reference time constant.
6. The method of claim 5 wherein said adjusting comprises incrementing the value of the variable resistive element.
7. The method of claim 5 wherein said comparing an RC time constant comprises:
setting a charge current based on the value of the variable resistive element;
charging the capacitive element for a predetermined time period at the charge current; and
comparing the voltage of the capacitive element to a reference voltage.
8. The Apparatus of claim 1 wherein the logic to calibrate the charge pump current of the phase-locked loop comprises logic to:
determine the gain of a VCO element (Kvco) of the phase-locked loop; and
set the charge pump current so that the charge pump current-Kvco product matches a predetermined value.
9. The method of claim 4 wherein the automatically calibrating the charge pump current of a charge pump circuit comprises:
determining the gain of a VCO element (Kvco) of the phase-locked loop; and
setting the charge pump current so that the charge pump current-Kvco product matches a predetermined value.
10. A method for calibrating a phase-locked loop, comprising:
setting a resistor value of a resistor component of an integration filter of the PLL to establish a predefined RC time constant for the integration filter; and
adjusting, after setting the resistor value, the open-loop gain of the PLL to replicate a control voltage step of a VCO component of the PLL developed at a first VCO frequency and a second VCO frequency.
11. The method of claim 10 wherein the control voltage is sensed and replicated by a comparator circuit.
12. The method of claim 10 wherein a charge pump current level of a charge pump component of the PLL is set based on said control voltage step.
13. The method of claim 10 wherein the resistor value is set at least in part to provide a predefined damping ratio.