Serializer architecture for serial communications
A serializer includes a first stage configured to convert m-bit-wide parallel data into n-bit-wide parallel data, where n is 2 x , m≧2 x+y , x is an integer of at least 1, and y is an integer of at least 1, where the first stage includes a memory unit configured to store the m-bit-wide parallel in response to a timing signal and a first multiplexer configured to output the n-bit-wide parallel data in response to a frequency-multiplied derivative of the timing signal, and a current mode logic (CML) multiplexer stage configured to convert the n-bit-wide parallel data into serial data on successive transitions of n phase-shifted versions of the frequency-multiplied derivative of the timing signal.
1. A current mode logic (CML) multiplexer configured to serialize n-bit-wide parallel data, comprising:
a) a load circuit coupled between a first supply node and a serial data node;
b) n selectors, wherein each of said selectors comprises: (i) a first transistor controllable by a bit of said n-bit-wide parallel data word, and coupled between a bias node and said serial data node; and (ii) a discharge path controllable by timing signals overlapping by a phase angle of about 360°/n; and
c) a bias circuit coupled to said load circuit, said discharge path, and said bias node, said bias circuit being configured to sink or source a predetermined current through said n selectors.
2. The CML multiplexer of claim 1 , wherein said load circuit comprises current source and diode loads.
3. The CML multiplexer of claim 1 , wherein said bias circuit is configured to receive a control voltage, and to provide a fixed current therefrom, the magnitude of said fixed current being a fixed multiple of the magnitude of said predetermined current.
4. The CML multiplexer of claim 1 , wherein n is an integer greater than or equal to four.
5. The CML multiplexer of claim 1 , wherein said discharge path comprises second and third transistors in series.
6. The CML multiplexer of claim 1 , wherein the first transistor is an NMOS transistor, the second transistor is an NMOS, and the third transistor is an NMOS transistor.
7. The CML multiplexer of claim 1 , wherein said timing signals comprise n phases of a clock signal.
8. The CML multiplexer of claim 1 , configured to receive differential parallel data and output differential serial data.