DS1807

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DS1807 ATTENUATOR CONFIGURATION Figure 3

ZERO-CROSSING DETECTION

The DS1807 provides many features for digitally controlled audio applications. Zero-crossing detection is

useful in eliminating “zipper noise,” which is commonly associated with digital potentiometers. Zipper

noise (because it sounds like a zipper) is caused by discrete wiper position changes on the resistor array.

These changes cause discontinuities in the audio output signal which are manifested as audible pops

heard at the output of the audio chain. If subsequent amplification follows the digital potentiometer, this

audible noise can be quite disturbing. The DS1807 minimizes zipper noise by allowing wiper position

changes only during zero-crossings of the input signal.

The zero-crossing detection feature can be enabled or disabled via software. The complete software

command for enabling or disabling zero-crossing is discussed in the section, “2-wire serial data bus.”

When enabled, the zero-crossing detection feature allows independent wiper changes within a 50

millisecond time window when the Hx and Lx (where x = 0 or 1) terminals have equal potentials. The 50

millisecond time window begins once the DS1807 has responded with an ACKNOWLEDGE after a

“write potentiometer “ command. The STOP condition is discussed in the following section.

If at 50 milliseconds the DS1807 has not detected a zero-crossing (Hx - Lx = 0), the wiper position of the

potentiometer(s) will change regardless of the state of the input signal.

When the zero-crossing detection feature is not activated, the DS1807 will allow movement to the new

wiper position as soon as the ACKNOWLEDGE condition has been issued by the master controlling

device.

The DS1807 is designed to provide the zero-crossing detection feature when initially powered. If this

feature is not to be used, it must be deactivated once the device has reached a fully powered condition.

2-WIRE SERIAL DATA BUS

The DS1807 supports a bi-directional 2-wire bus and data transmission protocol. A device that sends data

on the bus is defined as a transmitter, and a device receiving data as a receiver. The device that controls

the message is called a “master.” The devices that are controlled by the master are “slaves.” The bus must

be controlled by a master device which generates the serial clock (SCL), controls the bus access, and

generates the START and STOP conditions. The DS1807 operates as a slave on the 2-wire bus.

Connections to the bus are made via the open-drain I/O line, SDA, and the serial clock line, SCL.

The following bus protocol has been defined (See Figure 4).

§ Data transfer may be initiated only when the bus is not busy.

§ During data transfer, the data line must remain stable whenever the clock line is HIGH. Changes in

the data line while the clock line is high will be interpreted as control signals.