RESONANT RECHARGE FOR SYNCHRONOUS PULSED LASER OPERATION
Resonant recharge for synchronous pulsed laser operation. At least one example embodiment is a method of activating a laser diode, the method including: creating an oscillating voltage at a node between an inductor and a first capacitor, the oscillating voltage having a positive half-cycle and a negative half-cycle; charging a firing capacitor during a positive half-cycle of the oscillating voltage, the charging from the node and through a diode; and driving, during a negative half-cycle of the oscillating voltage, a pulse of current from the firing capacitance through a laser diode.
1 . A method of activating a laser diode, the method comprising:
creating an oscillating voltage at a node between an inductor and a first capacitor, the oscillating voltage having a positive half-cycle and a negative half-cycle;
charging a firing capacitor during the positive half-cycle of the oscillating voltage, the charging from the node and through a diode; and
driving, during the negative half-cycle of the oscillating voltage, a pulse of current from the firing capacitor through the laser diode.
2 . The method of claim 1 wherein creating the oscillating voltage at the node further comprises:
a) coupling a first lead of the inductor to a power source; and then
b) coupling the first lead of the inductor to ground; and
c) repeating steps a) and b) at a resonant frequency.
3 . The method of claim 1 wherein charging the firing capacitor further comprises charging the firing capacitor in parallel with charging the first capacitor during the positive half-cycle of the oscillating voltage.
4 . The method of claim 1 wherein driving the pulse of current from the firing capacitor further comprises discharging the firing capacitor through the laser diode and an electrically-controlled switch.
5 . A driver integrated circuit for controlling activation of a laser diode, the driver integrated circuit comprising:
a high-gate terminal, a low-gate terminal, a sense terminal, and a pulse-gate terminal;
a resonance controller coupled to the high-gate terminal and the low-gate terminal, the resonance controller configured to assert the high-gate terminal for a first duration within a switching period, and configured to assert the low-gate terminal for a second duration within the switching period; and
a firing controller coupled to the sense terminal and the pulse-gate terminal, the resonance controller configured to assert the pulse-gate terminal based on a signal sensed by way of the sense terminal.
6 . The driver integrated circuit of claim 5 further comprising:
a pulse-enable terminal;
the firing controller coupled to the pulse-enable terminal, and the firing controller further configured to assert the pulse-gate terminal when the pulse-enable terminal is asserted.
7 . The driver integrated circuit of claim 5 further comprising:
the signal sensed by way of the sense terminal is a signal indicative of voltage at a charge node; and
wherein the firing controller asserts the pulse-gate terminal only when the signal indicative of voltage indicates a voltage on the charge node is negative.
8 . The driver integrated circuit of claim 5 further comprising:
the signal sensed by way of the sense terminal is a signal indicative of current flow in an inductor-capacitor circuit; and
wherein the firing controller asserts the pulse-gate terminal only when the signal indicative of current flow indicates a voltage on a charge node is negative.
9 . The driver integrated circuit of claim 5 further comprising:
the resonance controller coupled to the sense terminal, and the resonance controller further configured to:
measure an attribute of oscillation on the by way of the sense terminal; and
control frequency of assertion of the high-gate terminal based on the attribute of oscillation.
10 . A driver integrated circuit for controlling activation of a laser diode, the driver integrated circuit comprising:
a source terminal, a switch-node terminal, a sense terminal, a ground terminal, and a pulse-gate terminal;
a high-side field-effect transistor (high-side FET) defining a drain coupled to the source terminal, a source coupled to the switch-node terminal, and a gate;
a low-side FET defining a drain coupled to the switch-node terminal, a source coupled to the ground terminal, and a gate;
a resonance controller coupled to the gate of the high-side FET and the gate of the low-side FET, the resonance controller configured to assert the gate of the high-side FET for a first duration within a switching period, and configured to assert the gate of the low-side FET during a second duration within the switching period; and
a firing controller coupled to the sense terminal and the pulse-gate terminal, the firing controller configured to sense an attribute of oscillation through the sense terminal, and assert the pulse-gate terminal based on the attribute of oscillation.
11 . The driver integrated circuit of claim 10 further comprising:
a pulse-enable terminal;
the firing controller coupled to the pulse-enable terminal, and the firing controller further configured to assert the pulse-gate terminal only when the pulse-enable terminal is asserted.
12 . The driver integrated circuit of claim 10 further comprising:
the attribute of oscillation is a signal indicative of voltage at a charge node; and
wherein the firing controller asserts the pulse-gate terminal only when the signal indicative of voltage indicates a voltage on the charge node is negative.
13 . The driver integrated circuit of claim 10 further comprising:
the attribute of oscillation is a signal indicative of current flow in an inductor-capacitor (LC) circuit; and
wherein the firing controller asserts the pulse-gate terminal only when the signal indicative of current flow indicates a voltage on a charge node is negative.
14 . The driver integrated circuit of claim 10 further comprising:
the resonance controller coupled to the sense terminal, and the resonance controller further configured to:
sense the attribute of oscillation by way of the sense terminal; and
control frequency of assertion of the gate of the high-side FET based on the attribute of oscillation.
15 . A system for light detecting and ranging, comprising:
an inductor-capacitor circuit (LC circuit) defining a first lead, a second lead, and a charge node between an inductor and a capacitor;
a high-side switch defining a first lead coupled to a power supply, a second lead coupled to the first lead of the LC circuit, and a control input;
a low-side switch defining a first lead coupled to the first lead of the LC circuit, a second lead coupled to the ground, and a control input;
a diode defining an anode coupled to the charge node, and a cathode;
a firing capacitor defining a first lead coupled to the cathode of the diode, and a second lead coupled to the to the ground;
a laser diode;
a pulse-control switch coupled to the firing capacitor and the laser diode, the pulse-control switch configured to couple the firing capacitor to the laser diode based on a control input;
a resonance controller coupled to the control inputs of the high-side switch, the low-side switch, and the pulse-control switch, the resonance controller configured to:
create an oscillating voltage at the charge node by control of the high-side switch and the low-side switch, the oscillating voltage having a frequency, a positive half-cycle, and a negative half-cycle; and
generate a laser pulse from the laser diode during the negative half-cycle of the oscillating voltage by making the pulse-control switch conductive.
16 . The system of claim 15 wherein when the resonance controller creates the oscillating voltage at the charge node, the resonance controller is further configured to:
a) assert the control input of the high-side switch to couple the first lead of the LC circuit to a power source; and then
b) assert the control input of the low-side switch to couple the first lead of the LC circuit to ground; and
c) repeat steps a) and b) at the frequency.
17 . The system of claim 15 further comprising a firing controller defining a pulse-enable input, the firing controller configured to assert the control input of the pulse-control switch only during the negative half-cycle of the oscillating voltage when the pulse-enable input is asserted.
18 . The system of claim 15 further comprising:
a current sensor associated with the charge node; and
the resonance controller coupled to the current sensor, and the resonance controller further configured to:
measure values indicative of current by way of the current sensor; and
control the frequency of the oscillating voltage based on the values indicative of current.
19 . The system of claim 15 :
wherein the high-side switch further comprises a field effect transistor (FET);
wherein the low-side switch further comprises a FET.
20 . The system of claim 15 wherein the high-side switch, the low-side switch, and the resonance controller all reside within a driver integrated circuit.