FX589P datasheet(12/18 Pages) CMLMICRO

12 / 18 page

S/N (dB) (noise in 8kHz bandwidth)

-5

-4

-3

-2

-1

56789

Tx and Rx DC coupled

Tx 5Hz, Rx DC coupled

Tx 5Hz, Rx 10Hz

Tx 5Hz, Rx 30Hz

Tx 5Hz, Rx 100Hz

Application Information ......

Fig.12 Effect of AC Coupling on Typical Bit-Error Rate

AC Coupling of Rx and Tx Signals

In practical applications, it will usually be possible

to arrange for any ac coupling between the FX589 Tx

Output and the frequency modulator to cut-off at a very

low frequency such as 5.0Hz, but ac coupling between

the receive discriminator and the input of the FX589

may need to have a shorter time-constant to avoid

problems from voltage steps at the output of the

discriminator when changing channels or when the

distant transmitter turns on.

For these reasons, as well as to maintain reasonable

BER, the optimum -3dB cut-off frequencies are around

5.0Hz in the Tx path and 20.0Hz in the Rx path.

The chart in Figure 12 (above) shows the typical

static Bit-Error-Rate performance of the FX589

operating under nominal conditions for various degrees

of ac coupling at the Rx Input and the Tx Output:

Data Rate =

8kb/s

5.0V

Tamb

25oC

Tx BT

0.3

Two Point Modulation

In a radio employing a frequency synthesiser, to

prevent the radio's PLL circuitry counteracting the

modulation process, and to provide a clean flat

modulation response down to dc, it is recommended

that a two-point modulation technique is employed

when using the FX589.

Figure 13 shows a suggested basic configuration

to provide a two-point modulation drive at 8kb/s from

the FX589 Tx Output using the FX019 (a CML product)

Digitally Controlled ‘Quad’ Amplifier Array.

The FX019 elements will provide individual setting-up,

calibration and dynamic control of modulation levels.

Level setting control of the amplifiers/attenuators of the

FX019 is via an 8-bit data word.

With reference to Figure 13:

The buffer amplifier is required to prevent loading of

the FX589 external RC circuit.

Stage B, with R1/R2, provides suitable signal and dc

levels for the VCO varactor; C1 is RF decoupling. The

drive level should be adjusted (digitally) to provide the

desired deviation.

Stage C, with R3/R4, provides the Reference

Oscillator drive (application dependant). This parameter

is set by adjusting for minimum ac signal on the PLL

control voltage with a low-frequency modulating signal

(inside the PLL bandwidth) applied.

Stage D, with its attendant components, could be

employed if a negative reference drive is required.

Stage A provides buffering and overall level control.

FX589P Datasheet(PDF) 12 Page - CML Microcircuits

FX589P Datasheet(HTML) 12 Page - CML Microcircuits

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

Datasheet Download

Link URL