Bias voltage circuit for biasing a transient suppression device and apparatus using same
View Patent ↗Embodiments provide a charge pump circuit which produces a bias voltage that is applied to a transient suppression device used to clamp both positive and negative transients on signal lines. The bias voltage can be set to a level that is above the sum of a DC voltage differential between positive and negative signal lines and the maximum signal voltage.
1. A circuit for biasing a signal line transient suppression device, the transient suppression device having a clamp voltage level at which it clamps voltage on at least a first signal line and a second signal line, a power voltage differential being provided between the first signal line and the second signal line, the circuit comprising:
an input network having a first input operable to be coupled to the first signal line and a second input operable to be coupled to the second signal line, the input network produces a direct current (DC) voltage between a positive input line and a negative input line from the power voltage differential between the first signal line and the second signal line; and
a bias voltage generator having a positive input connected to the positive input line of the input network and a negative input connected to the negative input line of the input network, the bias voltage generator circuit operable to produce a DC voltage output between a positive output and a negative output, the positive output coupled to a positive side of the transient suppression device, the negative output coupled to a negative side of the transient suppression device, the DC output voltage is at a level above the sum of a maximum amplitude of the power voltage differential between the first and second signal lines and a signal level between the first and second signal lines, wherein the input network comprises:
a first input impedance coupled between the first input and a center point between a first diode pair coupled in series between the positive line and the negative line of the input network; and
a second input impedance coupled between the second input and a center point between a second diode pair coupled in series between the positive line and the negative line of the input network.
2. The circuit of claim 1 , wherein the bias voltage generator circuit comprises a charge pump circuit.
3. The circuit of claim 2 , wherein the charge pump circuit comprises:
an oscillator that provides an output between a positive output and a negative output;
a rectifier circuit capacitively coupled to the positive and negative outputs of the oscillator and that rectifies the output of the oscillator to provide the DC output voltage; and
an output filter capacitance coupled across an output of the rectifier circuit and configured to be in parallel with the transient suppression device.
4. The circuit of claim 1 , further comprising:
a third input operable to be coupled to a third signal line having a power voltage polarity in common with the first signal line, a third input impedance coupled between the third input and the center point of the first diode pair; and
a fourth input operable to be coupled to a fourth signal line having a power voltage polarity in common with the second signal line, a fourth input impedance coupled between the fourth input and the center point of the second diode pair.
5. The circuit of claim 4 , wherein the first input and the second input are operable to be connected to an Ethernet bus operated in accordance with an IEEE 802.3 specification.