P9225-R Datasheet

© 2018 Integrated Device Technology, Inc.

20

November 12, 2018

9. Communication Interface

9.1 Modulation/Communication

Receiver-to-transmitter communication is accomplished by modulating the load seen by the receiver's inductor; the communication is purely

digital and logic 1’s and 0’s ride on top of the power signal that exists between the two coils. Modulation is done with amplitude-shift keying

(ASK) modulation using internal switches to connect external capacitors from AC1 and AC2 to ground (see Figure 15) with a bit rate of 2Kbps.

To the transmitter, this appears as an impedance change, which results in measurable variations of the transmitter’s output waveform. The

power transmitter detects this as a modulation of coil current/voltage to receive the packets.

As required by the WPC, the P9225-R uses a differential bi-phase encoding scheme to modulate data bits onto the power signal. A clock

frequency of 2kHz is used for this purpose. A logic ONE bit is encoded using two narrow transitions, whereas a logic ZERO bit is encoded using

one wider transition as shown below:

Figure 16. Bit Encoding Scheme

tCLK

ONE

ZERO

ONE

ZERO

ONE

ONE

ZERO

ZERO

9.2 Byte Encoding for ASK

Each byte in the communication packet comprises 11 bits in an asynchronous serial format, as shown in Figure 17.

Figure 17. Byte Encoding Scheme

Start

Stop

Parity

b0

1

2

3

4

5

6

7

b

b

b

b

b

b

b

Each byte has a start bit, 8 data bits, a parity bit, and a single stop bit.

9.3 Packet Structure

The P9225-R communicates with the base station via communication packets. Each communication packet has the following structure:

Figure 18. Communication Packet Structure

Preamble

Header

Message

Checksum