Oscillator circuit with RF suppression
An oscillator circuit includes a phase-locked loop, a crystal resonator, first and second capacitors, and first and second impedance elements. The phase-locked loop is coupled between a first node and a second node. The crystal resonator is also coupled between the first node and the second node. The first capacitor is coupled between the first node and ground, and the second capacitor is coupled between the second node and ground. The first impedance element is coupled in a first circuit path from the first node to ground through the first capacitor. The second impedance element is coupled in a second circuit path from the second node to ground through the second capacitor.
1. An arrangement for use in an electricity meter comprising:
a metrology circuit operably coupled to detect and measure electrical signals provided to a load, the metrology circuit including a processing unit configured to generate metering information based on the measured electrical signals, the processing unit using clocking signals to maintain a real-time clock and to generate clock signals for metrology circuit operations;
a phase-locked loop circuit configured to provide the clocking signals to the metrology circuit processing unit, the phase-locked loop circuit having a reference frequency input;
an oscillator circuit including a crystal resonator coupled between a first node and a second node, and a further element coupled between the first node and the second node, a first capacitor coupled between the first node and ground, and a first impedance element in a first circuit path from the first node to ground through the first capacitor; and
wherein each circuit path through the first node, the first capacitor and the second node passes through the first impedance element,
wherein the first impedance element is configured to attenuate RF signals that are radiated onto at least portions of the oscillator circuit; and
wherein the second node is electrically directly coupled to the reference frequency input of the phase-locked loop.
2. The arrangement of claim 1 , wherein the first impedance element comprises a ferrite bead.
3. The arrangement of claim 1 , wherein the further element comprises an amplifier.
4. The arrangement of claim 1 , wherein the oscillator circuit further includes a second impedance element in a second circuit path from the second node to ground through a second capacitor.
5. The arrangement of claim 4 , wherein the first impedance element and the second impedance element are substantially identical.
6. The arrangement of claim 4 , wherein the first impedance element and the second impedance element comprise ferrite beads.
7. The arrangement of claim 6 , further comprising an RF communication transmission device configured to transmit metering information to a remote location, the radiated RF signals originating from the RF communication transmission device.
8. The arrangement of claim 7 , further comprising a first rectifying element coupled between the first node and ground, and a second rectifying element coupled between the second node and ground, and wherein each circuit loop through the first rectifying element and one of the first capacitor and the second capacitor includes at least one of the ferrite beads.
9. The arrangement of claim 8 , wherein a serial circuit path from the first node to ground through the first rectifying element does not include any ferrite beads.
10. The arrangement of claim 9 , wherein every serial circuit path starting at the first node, ending at the second node, and including the first capacitor intermediate thereof, passes through the first impedance element.
11. The arrangement of claim 6 , further comprising a first rectifying element coupled between the first node and ground, and a second rectifying element coupled between the second node and ground, and wherein each circuit loop through the first rectifying element and one of the first capacitor and the second capacitor includes at least one of the ferrite beads.
12. The arrangement of claim 11 , wherein the crystal resonator is directly electrically coupled between the first node and the second node.
13. The arrangement of claim 12 , wherein a serial circuit path from the first node to ground through the first rectifying element does not include any ferrite beads.
14. The arrangement of claim 1 , wherein every serial circuit path starting at the first node, ending at the second node, and including the first capacitor intermediate thereof, passes through the first impedance element.