Charge pump for PLL/DLL
View Patent ↗A charge pump for use in a Phase Locked Loop/Delay Locked Loop minimizes static phase error through the use of an operational amplifier. The operational amplifier also mitigates the effects of low power supply voltage.
1. A charge pump comprising:
pull-up circuitry that comprises a current source and a controlled transistor having a gate adapted for connection to a first input signal for being controlled thereby, the pull-up circuitry electrically connected between a positive voltage supply and a charge pump output node;
pull-down circuitry that comprises a current source and a controlled transistor having a gate adapted for connection to a second input signal for being controlled thereby, the pull-down circuitry electrically connected between a ground voltage supply and the charge pump output node, the first and second input signals being derived from up and down signals, respectively;
a reference current source;
a plurality of programmable transistors that comprise pairs of transistors in series, both the reference current source and the plurality of programmable transistors each configured to control the current in at least one of the current sources of the pull-up and pull-down circuitries, and each of the pairs of transistors comprise a switch-functioning transistor and a current mirror transistor, and the switch-functioning transistor having a gate electrically connected to a fuse circuit; and
a capacitor electrically connected to the charge pump output node.
2. The charge pump as claimed in claim 1 further comprising additional pull-up circuitry and additional pull-down circuitry connected at an additional node.
3. The charge pump as claimed in claim 2 wherein the additional pull-up circuitry and the pull-up circuitry have corresponding transistors with source and drain terminals connected in the same manner, and the additional pull-down circuitry and the pull-down circuitry have corresponding transistors with source and drain terminals connected in the same manner.
4. The charge pump as claimed in claim 3 wherein a gate of a controlled transistor in the additional pull-up circuitry is connected to a first voltage supply, and a gate of a controlled transistor in the additional pull-down circuitry is connected to a second voltage supply.
5. The charge pump as claimed in claim 3 wherein the additional pull-up circuitry and the pull-up circuitry have correspondingly same sized transistors, and the additional pull-down circuitry and the pull-down circuitry have correspondingly same sized transistors.
6. The charge pump as claimed in claim 1 wherein the reference current source forms a part of the plurality of programmable transistors.
7. The charge pump as claimed in claim 1 further comprising a startup circuit connected to the charge pump output node.
8. The charge pump as claimed in claim 7 wherein the startup circuit comprises a MOS device having a source connected to a voltage supply and a gate connected to a startup control signal.
9. The charge pump as claimed in claim 8 wherein the voltage supply is the ground voltage supply.
10. The charge pump as claimed in claim 8 wherein the startup circuit further comprises a source follower transistor that is connected in series with the MOS device.
11. The charge pump as claimed in claim 10 wherein the voltage supply is the ground voltage supply and the source follower transistor is connected to the charge pump output node.
12. The charge pump as claimed in claim 1 further comprising an operational amplifier having two inputs and an output, the operational amplifier configured to reduce phase error, one of the inputs of the operational amplifier connected to the charge pump output node.
13. The charge pump as claimed in claim 12 further comprising a startup circuit to establish a predetermined voltage level at the charge pump output node during startup.
14. The charge pump as claimed in claim 12 further comprising additional pull-up circuitry and additional pull-down circuitry connected at an additional node.
15. The charge pump as claimed in claim 14 wherein the additional pull-up circuitry and the pull-up circuitry have corresponding transistors with source and drain terminals connected in the same manner, and the additional pull-down circuitry and the pull-down circuitry have corresponding transistors with source and drain terminals connected in the same manner.
16. The charge pump as claimed in claim 14 wherein the other input of the operational amplifier is connected to the additional node.
17. The charge pump as claimed in claim 12 wherein the output of the operational amplifier is connected to either the current source of the pull-down circuitry or the current source of the pull-up circuitry.
18. The charge pump as claimed in claim 12 wherein the operational amplifier has an output range substantially from rail to rail.
19. The charge pump as claimed in claim 12 wherein the operational amplifier comprises two differential input stages.