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TYPICAL APPLICATIONS

USING THE ES SERIES TRANSMITTER FOR ANALOG APPLICATIONS

The ES Series is an excellent choice for sending analog information, including

audio. The ability of the ES to transmit combinations of analog and digital content

opens many new opportunities for design creativity.

Simple or complex analog signals within the specified audio bandwidth and input

levels may be connected directly to the transmitter’s DATA line. The transmitter

input is high impedance (500k

Ω) and can be directly driven by a wide variety of

sources, ranging from a single frequency to complex content, such as audio.

and should be AC-coupled into the DATA line. The size of the coupling capacitor

should be large enough to ensure the passage of all desired frequencies. Since

the modulation voltage applied to the DATA line determines the carrier deviation,

distortion can occur if the DATA line is over-driven. The actual level of the input

waveform should be adjusted to achieve optimum in-circuit results.

USING THE ES SERIES TRANSMITTER FOR DIGITAL APPLICATIONS

The ES Series transmitter is equally capable at accommodating digital data. The

transmitter input is high impedance (500k) and can be directly driven by a wide

variety of sources including microprocessors and encoder ICs.

When the transmitter will be used to transmit digital data, the DATA line is best

driven from a 3 to 5V source. The transmitter is designed to give an average

deviation of 115kHz with a 5V square wave input, and 75kHz with 3V square

wave input. Either choice will achieve maximum performance.

Data adhering to different electrical level standards, such as RS-232, will require

buffering or conversion to logic level voltages. In the case of RS-232, such

buffering is easily handled with widely available ICs, such as the MAX232, which

is used on the ES Series Master Development System. The Linx SDM-USB-QS

can be used to convert between USB compliant signals and logic level voltages.

0.1µF

0-Vcc Audio Source

PDN

LADJ

VCC

LO_V_D

/CLK SE

/CLK

GND

DATA

ANT

GND

1

2

3

4

56

7

8

9

10

Figure 10: AC Coupling An Audio Source

PROTOCOL GUIDELINES

While many RF solutions impose data formatting and balancing requirements,

Linx RF modules do not encode or packetize the signal content in any manner.

The received signal will be affected by such factors as noise, edge jitter, and

interference, but it is not purposefully manipulated or altered by the modules.

This gives the designer tremendous flexibility for protocol design and interface.

Despite this transparency and ease of use, it must be recognized that there are

distinct differences between a wired and a wireless environment. Issues such as

interference and contention must be understood and allowed for in the design

process. To learn more about protocol considerations, we suggest you read Linx

Application Note AN-00160.

Errors from interference or changing signal conditions can cause corruption of

the data packet, so it is generally wise to structure the data being sent into small

packets. This allows errors to be managed without affecting large amounts of

data. A simple checksum or CRC could be used for basic error detection. Once

an error is detected, the protocol designer may wish to simply discard the corrupt

data or implement a more sophisticated scheme to correct it.

INTERFERENCE CONSIDERATIONS

The RF spectrum is crowded and the potential for conflict with other unwanted

sources of RF is very real. While all RF products are at risk from interference, its

effects can be minimized by better understanding its characteristics.

Interference may come from internal or external sources. The first step is to

eliminate interference from noise sources on the board. This means paying

careful attention to layout, grounding, filtering, and bypassing in order to

eliminate all radiated and conducted interference paths. For many products, this

is straightforward; however, products containing components such as switching

power supplies, motors, crystals, and other potential sources of noise must be

approached with care. Comparing your own design with a Linx evaluation board

can help to determine if and at what level design-specific interference is present.

External interference can manifest itself in a variety of ways. Low-level

interference will produce noise and hashing on the output and reduce the link’s

overall range.

High-level interference is caused by nearby products sharing the same

frequency or from near-band high-power devices. It can even come from your

own products if more than one transmitter is active in the same area. It is

important to remember that only one transmitter at a time can occupy a

frequency, regardless of the coding of the transmitted signal. This type of

interference is less common than those mentioned previously, but in severe

cases it can prevent all useful function of the affected device.

Although technically it is not interference, multipath is also a factor to be

understood. Multipath is a term used to refer to the signal cancellation effects

that occur when RF waves arrive at the receiver in different phase relationships.

This effect is a particularly significant factor in interior environments where

objects provide many different signal reflection paths. Multipath cancellation

results in lowered signal levels at the receiver and, thus, shorter useful distances

for the link.