5

SL1710

Fig.4 Typical RF input impedance

APPLICATION NOTES

These application notes should be read in conjunction with

the circuit diagram Fig 3. and the PCB layout illustrated in Figs

9 and 10. An alternative oscillator configuration using a SAW

Resonator is shown in the circuit diagram Fig. 11 and the PCB

layout illustrated in Figs 12 and 13. These boards have been

designed to permit the initial evaluation of the SL1710

performance.

VARACTOR TUNED

The application detailed in Fig.3 uses a synthesised VCO.

The tuning range of the oscillator is;

Varactor line Voltage.

Oscillator Frequency

5 Volts

458MHz

30 Volts

504MHz

This configuration gives a VCO sensitivity of 1.84MHz/

Volt. The inductor L1 is a 12nF surface mount component.

Different VCO centre frequencies and sensitivities can be

achieved by changing the values of L1, C12 and C13.

The VCO frequency is controlled by the SP5611

RF

input to the synthesiser is from the SL1710 prescaler outputs

via RF inductors L3 and L4.

SAW RESONATOR OSCILLATOR

The application detailed in Fig. 11 shows an SL1710 with

a SAW Resonator controlled oscillator. In this instance the

frequency accuracy

and stability of the oscillator are

determined by the Saw Resonator. The PCB detailed in Figs.

12 and 13 is designed to accommodate the following SAWR;

Manufacturer

Part No

MURATA

SAR479.45MB10X200

PRESCALER OUTPUTS

The VCO frequency/32 is available at the differential

prescaler outputs pins 10 and 11. This enables the on board

VCO to be synthesised via a PLL.

VCO DISABLE

The on-chip oscillator can be disabled by connecting the

VCO Disable (pin 15) to ground and enabled by connecting the

pin to V

CC

via a 4K7 pull up resistor.

AGC

The DC voltage measured at TP1 should be adjusted using

VR1 to read 2.5 volts with respect to V

EE

. this voltage equates

to the nominal centre of the AGC control curve. The control

voltage applied to pin 1 can be varied between 0.5 Volts

(maximum gain) and V

CC

-0.5 Volts minimum gain)

0.5

0.2

1

0

+j0.2

+j0.5

+j1

+j2

+j5

2

5

–j5

–j2

–j1

–j0.5

–j0.2

START 350 MHz

STOP 650 MHz

Marker

1 480MHz

Zreal

= 75.7

Zimag

= –36.4