Pulse amplitude modulation (PAM) encoding for a communication bus
Pulse amplitude modulation (PAM) encoding for a communication bus is disclosed. In particular, various two-wire communication buses may encode bits using three-level PAM (PAM-3) or five-level PAM (PAM-5) to increase bit transmission without requiring increases to clock frequencies or adding additional pins. Avoiding increases in clock frequencies helps reduce the risk of electromagnetic interference (EMI), and avoiding use of extra pins avoids cost increases for integrated circuits (ICs).
1. An integrated circuit (IC) comprising:
a bus interface coupled to a communication bus;
a clock source coupled to the bus interface; and
a control circuit configured to:
send a clock signal derived from the clock source and having a parity bit embedded therein over a clock line of the communication bus through the bus interface;
send a pulse amplitude modulated (PAM) data signal over a data line of the communication bus; and
sample the data line for incoming signals at a rate at least three times a frequency of the clock signal.
2. The IC of claim 1 , wherein the control circuit is configured to provide eight bits of data and the parity bit across a single clock cycle of the clock source.
3. The IC of claim 1 , wherein the bus interface is configured to be coupled to one of a radio frequency front end (RFFE) bus, a system power management interface (SPMI) bus, or an I3C bus.
4. The IC of claim 2 , wherein the PAM data signal comprises six bits of data per clock cycle.
5. The IC of claim 4 , wherein the clock signal comprises two bits of data in addition to the parity bit.
6. The IC of claim 1 , wherein the control circuit is configured to encode the PAM data signal using a three-level PAM (PAM-3) encoding technique.
7. The IC of claim 1 , wherein the control circuit is configured to encode the parity bit into the clock signal by setting a duty cycle of the clock signal.
8. The IC of claim 1 , wherein the bus interface comprises a single-ended bus interface.
9. The IC of claim 1 , wherein the bus interface comprises a differential bus interface.
10. The IC of claim 1 integrated into a device selected from the group consisting of: a set top box; an entertainment unit; a navigation device; a communications device; a fixed location data unit; a mobile location data unit; a global positioning system (GPS) device; a mobile phone; a cellular phone; a smart phone; a session initiation protocol (SIP) phone; a tablet; a phablet; a server; a computer; a portable computer; a mobile computing device; a wearable computing device; a desktop computer; a personal digital assistant (PDA); a monitor; a computer monitor; a television; a tuner; a radio; a satellite radio; a music player; a digital music player; a portable music player; a digital video player; a video player; a digital video disc (DVD) player; a portable digital video player; an automobile; a vehicle component; avionics systems; a drone; and a multicopter.
11. An integrated circuit (IC) comprising:
a bus interface coupled to a communication bus;
a control circuit configured to:
receive a clock signal having a parity bit embedded therein over a clock line of the communication bus through the bus interface; and
receive a pulse amplitude modulated (PAM) data signal over a data line of the communication bus; and
a clock source operating with at least three times a frequency of the clock signal.
12. The IC of claim 11 , wherein the control circuit is further configured to sample the PAM data signal using the clock source at least three times during a period of the clock signal.
13. The IC of claim 11 , wherein the bus interface comprises a system power management interface (SPMI) bus interface, a radio frequency front end (RFFE) bus interface, or an I3C bus interface.
14. The IC of claim 11 , wherein the control circuit is configured to receive a five-level PAM (PAM-5) encoded data signal over the data line.
15. The IC of claim 11 , wherein the control circuit is configured to receive a three-level PAM (PAM-3) encoded data signal over the data line.
16. The IC of claim 11 , wherein the control circuit is configured to decode six bits from the PAM data signal.
17. The IC of claim 11 , wherein the control circuit is configured to decode two bits and the parity bit from the clock signal.
18. The IC of claim 11 , wherein the clock source comprises a phase-locked loop (PLL).
19. The IC of claim 11 integrated into a device selected from the group consisting of: a set top box; an entertainment unit; a navigation device; a communications device; a fixed location data unit; a mobile location data unit; a global positioning system (GPS) device; a mobile phone; a cellular phone; a smart phone; a session initiation protocol (SIP) phone; a tablet; a phablet; a server; a computer; a portable computer; a mobile computing device; a wearable computing device; a desktop computer; a personal digital assistant (PDA); a monitor; a computer monitor; a television; a tuner; a radio; a satellite radio; a music player; a digital music player; a portable music player; a digital video player; a video player; a digital video disc (DVD) player; a portable digital video player; an automobile; a vehicle component; avionics systems; a drone; and a multicopter.
20. A computing system comprising:
a communication bus;
a first integrated circuit (IC) comprising:
a first bus interface coupled to the communication bus;
a clock source coupled to the first bus interface; and
a first control circuit configured to:
send a clock signal derived from the clock source and having a parity bit embedded therein over a clock line of the communication bus through the first bus interface; and
send a pulse amplitude modulated (PAM) data signal over a data line of the communication bus; and
a second IC comprising:
a second bus interface coupled to the communication bus; and
a second control circuit configured to:
receive the clock signal having the parity bit embedded therein; and
receive the PAM data signal.
21. The computing system of claim 20 , wherein the second IC comprises a second clock source operating at a frequency at least three times a frequency of the clock signal.
22. The computing system of claim 20 , wherein the first control circuit is further configured to allow programmable selection of clock-to-data phase and polarity relationships.