Apparatus and methods of reducing pre-emphasis voltage jitter

1. A transmitter circuit comprising:

a first current source, wherein the first current source comprises a pull-up current source;

a first filter coupled between the first current source and a first node

a second filter coupled between the first current source and a second node;

a second current source, wherein the second current source comprises a pull-down current source;

a third filter coupled between the second current source and a third node;

a fourth filter coupled between the second current source and a fourth node; and

a driver switch circuit coupled to the first, second, third and fourth nodes, wherein the driver switch circuit comprises a main driver circuit connected to the first and third nodes and a pre-emphasis driver circuit connected to the second and fourth nodes.

2. The transmitter circuit of claim 1 , wherein the first, second, third, and fourth filters each comprise a low-pass filter.

3. The transmitter circuit of claim 1 , wherein the pull-up current source comprises a PMOS current source, and wherein the pull-down current source comprises an NMOS current source.

4. The transmitter circuit of claim 1 , wherein the main driver circuit is configured to receive a digital data signal, and wherein the pre-emphasis driver circuit is configured to receive a pre-emphasis signal which is a phase shifted and scaled version of the digital input signal.

5. The transmitter circuit of claim 4 , wherein the driver switch circuit is configured to add the pre-emphasis signal to the digital data signal and output a resulting signal.

6. The transmitter circuit of claim 1 , wherein the main driver circuit comprises:

first and second transistors connected in series between the first and third nodes;

a first output node between the first and second transistors;

third and fourth transistors connected in series between the first and third nodes;

a second output node between the third and fourth transistors; and

a resistance connected between the first and second output nodes.

7. The transmitter circuit of claim 6 , wherein the pre-emphasis driver circuit comprises:

fifth and sixth transistors connected in series between the second and fourth nodes, wherein in the first output node is connected between the fifth and sixth transistors; and

seventh and eighth transistors connected in series between the second and fourth nodes, wherein the second output node is connected between the seventh and eight transistors.

8. The transmitter circuit of claim 7 , wherein the resistance comprises:

first and second resistors connected in series between the first and second output nodes; and

a common-mode voltage node between the first and second resistors.

9. The transmitter circuit of claim 8 , further comprising a common-mode voltage source connected between the common-mode voltage node and ground.

10. The transmitter circuit of claim 7 , wherein the first, third, fifth and seventh transistors are PMOS transistors, and wherein the second, fourth, sixth and eighth transistors are NMOS transistors.

11. A method of driving a transmission signal with pre-emphasis having minimal voltage jitter, the method comprising:

receiving a digital data signal;

generating a pre-emphasis signal which is a phase shifted and scaled version of the digital data signal;

inputting the digital data signal and the pre-emphasis signal to a driver switch circuit;

applying low-pass filtering to current sources for the driver switch circuit; and

generating an output signal by adding the pre-emphasis signal to the digital data signal in the driver switch circuit.

12. The method of claim 11 , wherein the current sources comprise a pull-up current source and a pull-down current source, and wherein the low-pass filtering is applied by a first low-pass filter connected between the pull-up current source and the driver switch circuit, a second low-pass filter connected between the pull-down current source and the driver switch circuit, a third low-pass filter connected between the pull-up current source and the driver switch circuit, and a fourth low-pass filter connected between the pull-down current source and the driver switch circuit.

13. The method of claim 12 , wherein the driver switch circuit comprises a main driver circuit connected to the first and third nodes and a pre-emphasis driver circuit connected to the second and fourth nodes.

14. The method of claim 13 , wherein the main driver circuit comprises:

first and second transistors connected in series between the first and third nodes;

a first output node between the first and second transistors;

third and fourth transistors connected in series between the first and third nodes;

a second output node between the third and fourth transistors; and

a resistance connected between the first and second output nodes.

15. The method of claim 14 , wherein the pre-emphasis driver circuit comprises:

fifth and sixth transistors connected in series between the second and fourth nodes, wherein in the first output node is connected between the fifth and sixth transistors; and

seventh and eighth transistors connected in series between the second and fourth nodes, wherein the second output node is connected between the seventh and eight transistors.

16. The method of claim 15 , wherein the resistance comprises:

first and second resistors connected in series between the first and second output nodes; and

a common-mode voltage node between the first and second resistors.

17. An integrated circuit comprising:

a transmitter which is configured to receive a digital data signal and generate a pre-emphasis signal which is a phase shifted and scaled version of the digital data signal;

a driver switch circuit for the transmitter which is configured to add the pre-emphasis signal to the digital data signal so as to generate an output signal; and

a plurality of low-pass filters connected between current sources and the driver switch.

18. The integrated circuit of claim 17 , wherein the integrated circuit comprises a field-programmable gate array which includes a plurality of programmable logic array blocks, and wherein the transmitter is included as part of a transceiver channel circuit which is coupled to the plurality of programmable logic array blocks.