Oscillator devices and methods thereof
Oscillator devices and methods of operating such oscillator devices are disclosed. The oscillator devices include a current source, and an oscillation module to provide a clock signal. The frequency of the clock signal depends on the relationship between a threshold voltage of a transistor at the oscillation module and the current level provided by the current source. The transistor at the oscillation module is matched to a transistor at the current source so that the frequency of the clock signal is relatively insensitive to changes in device temperature.
1. A method comprising:
applying a first current to charge a capacitor to a first voltage level during a first interval, the first voltage level dependent on a first threshold voltage;
generating a first clock signal interval in response to the capacitor charge reaching the first threshold voltage;
reversing a polarity of the capacitor in response to the capacitor charge reaching the first threshold voltage during the first interval;
applying the first current to charge the capacitor to a second voltage level during a second interval, the second voltage level dependent on a second threshold voltage; and
generating a second clock signal interval in response to the capacitor charge reaching the second threshold voltage.
2. The method of claim 1 , wherein generating the first clock signal comprises:
asserting a first signal based on a charge of the capacitor;
applying the first signal to a first input of a flip-flop;
asserting a second signal based on the charge of the capacitor; and
applying the second signal to a second input of the flip-flop.
3. The method of claim 1 , wherein generating the first clock signal comprises providing a first current to a first inverter in response to the capacitor charge reaching the first threshold voltage.
4. The method of claim 3 , further comprising providing an inverted representation of a signal from the first inverter to an input of a latch.
5. The method of claim 4 , wherein the latch comprises a set-reset flip flop.
6. The method of claim 5 , wherein generating the first clock signal comprises providing a second current to a second inverter in response to switching the polarity of the capacitor.
7. The method of claim 1 , further comprising reversing the polarity of the capacitor in response to the capacitor charge reaching the second threshold voltage during the second interval.
8. A device, comprising
a current source comprising:
a first transistor comprising a first current electrode coupled to a first voltage reference, a second current electrode coupled to a second voltage reference, and a control electrode coupled to the second voltage reference;
a second transistor comprising a first current electrode coupled to the first voltage reference, a second current electrode coupled to the control electrode of the first transistor, and a control electrode coupled to the first current electrode of the first transistor; and
an output coupled to the first current electrode of the first transistor;
a switching module comprising:
a capacitor comprising a first current electrode responsive to a voltage at the output of the current source during a first interval and a second current electrode responsive to a voltage at the output of the current source during a second interval; and
a first control module comprising a third transistor that is matched with the first transistor, the third transistor comprising a first current electrode coupled to the first voltage reference, a second current electrode coupled to the second voltage reference, and a control electrode coupled to the first current electrode of the capacitor;
a second control module comprising a fourth transistor that is matched with the first transistor, the fourth transistor comprising a first current electrode coupled to the first voltage reference, a second current electrode coupled to the second voltage reference, and a control electrode coupled to the second current electrode of the capacitor; and
a latch comprising a first input coupled to the first current electrode of the third transistor, a second input coupled to the first current electrode of the fourth transistor, and a first output configured to provide a periodic signal based on a first signal at the first input and a second signal at the second input.
9. The device of claim 8 , wherein the switching module further comprises:
a fifth transistor comprising a first current electrode coupled to the first voltage reference, a second current electrode coupled to the second current electrode of the capacitor, and a control electrode coupled to a second output of the latch; and
a sixth transistor comprising a first current electrode coupled to the first voltage reference, a second current electrode coupled to the first current electrode of the capacitor, and a control electrode coupled to the first output of the latch.
10. The device of claim 9 , wherein the switching module further comprises:
a seventh transistor comprising a first current electrode coupled to the second current electrode of the capacitor, a second current electrode coupled to the second voltage reference, and a control electrode coupled to the second output of the latch; and
an eighth transistor comprising a first current electrode coupled to the first current electrode of the capacitor, a second current electrode coupled to the second voltage reference, and a control electrode coupled to the first output of the latch.
11. The device of claim 8 , wherein the latch is a set-reset flip flop.
12. The device of claim 8 further comprising a plurality of resistors coupled in series between the second current electrode of the second transistor and the second voltage reference.
13. The device of claim 12 wherein a first of the plurality of resistors comprises a N doped poly resistor and a second of the plurality of resistors is a P doped poly resistor.
14. The device of claim 8 , wherein the first, second and third transistors are CMOS transistors.