15

Preliminary Information

SL1925

SL1925 Demo Board

The demo board contains an SL1925 direct conversion

IC and SP5769 synthesiser. Reference to the

specifications for each device may be required in

conjunction with these notes.

The board contains all components necessary to

demonstrate operation of the SL1925. The schematic

and PCB layout of the board are shown in figures 16, 17

and 18. The SP5769 synthesiser is provided to control

each of the oscillators of the SL1925.

Supplies

The board must be provided with the following supplies:

5V for the synthesiser, 30V for the varactor line and 5V

for the SL1925.

The supply connector is a 5 pin 0.1” pitch pin header.

The order of connections is 5V - GND - 30V - GND - 5V

which feeds directly to the SP5769 synthesiser. This

connects to a standard 4 way cable which is supplied

with the interface box.

Operating Instructions

1. Software

Use the Mitel Semiconductor synthesiser software. Pull

It is suggested that the charge pump setting 130uA is

used, and the reference divider is set to 32. These

settings give a small loop bandwidth (i.e. 100’s Hz),

which allows detailed phase noise measurements of the

oscillators to be taken, if desired.

2. VCO control

The two VCO’s are selected by toggling port P1 on the

synthesiser which in turn toggles the LOsel input of the

SL1925.

VCOS is switched on (and hence VCOV off) by clicking

P1 on - a tick will appear.

VCOS oscillates at twice the LO frequency (lower band)

and is then divided by two to provide the required LO

frequency in the range 950MHz to 1500MHz

approximately.

VCOV is switched on (and hence VCOS off) by clicking

P1 off - no tick.

VCOV oscillates at the LO frequency (upper band) in the

range 1450MHz to 2150MHz approximatley.

3. AGC control

The AGC input of the SL1925 which determines the

conversion gain should be controlled by application of an

external voltage to the AGC pin, TP1.

Caution: Care should be taken to ensure the chip is

powered ON when +ve voltages are applied to the AGC

input so as to avoid powering the chip up via the ESD

protection diode of the AGC input. It is recommended

that a low current limit is set on the external source used.

4. Free running the VCO’s

Select the required VCO using port P1 and then using

the software choose an LO frequency which is above the

maximum frequency capability of the oscillator. 3GHz

is suggested for both oscillators. Under this condition the

varactor control voltage is pumped to its maximum

value, i.e. to the top of the band. The oscillator frequency

may be manually tuned by varying the 30V supply.