13

SL1714

Programming of Synthesisers

A SP5611 synthesiser is used to set the frequency of the

SL1714 VCO (480MHz). Since the SL1714 incorporates a

divide by 32 the synthesised frequency that the SP5611 must

be programmed to is 480/32=15MHz.

Example

a) To program the SL1714 to 480MHz.

I2C Byte

Hex Code

Byte 1 (address)

C2

Byte 2 (programmable divider 8 MSBs)

00

Byte 3 (programmable divider 8 LSBs)

F0

Byte 4 (control data)

CE

Byte 5 (port data)

00

C2 is the address byte (byte 1).

0F00 is the programmable divider information (bytes 2 and 3).

CE is the control data information (byte 4).

**Note - the programmable divider information should be

set to program 480MHz /32 = 15MHz since the SL1714

provides a divide by 32 prescaler output rather than the VCO

carrier frequency.

It is not possible to program the VCO to 479.5MHz when

using a 7.8125kHz phase comparator frequency. The mini-

mum step size is 7.8125KHz x 8 (RF prescaler inside SP5611)

x 32 (SL1714 output prescaler) = 2MHz.

If the reference divider is set to 1024 mode (3.90625kHz

phase comparator frequency), the minimum step size will be

1MHz.

This may be achieved by programming the control byte to

CC and modifying the programmable divider information for

the new step size.

SL1714 Operation

The SL1714 will mix an IF input with its own local oscillator.

This is controlled as above via a SP5611 synthesiser.

Normally the VCO will be set to the same frequency as the

IF input, and the signal mixed directly down to baseband.

Alternatively, a CW RF source may be fed into the input of

the SL1714 which is deliberately offset from the VCO. By

varying the offset from 0-20MHz and monitoring the I and Q

channel baseband outputs, the flatness response of the chip/

output filter can be measured.

The SL1714 oscillator may also be disabled by setting the

ON-VCO-OFF switch to the OFF position.

An AGC voltage adjust pot marked AGC ADJUST is

provided, together with a test point.

Measurement of Gain and Phase Match.

a) Synthesise the required frequency (480MHz is used in the

example above).

b) Connect an RF signal generator to the input.

c)Input a signal which should give an output of approx 0dBm

(0.707V p-p), in combination with the appropriate AGC

setting.

d) Connect a vector voltmeter to the BUFFERED outputs

when using 50

Ω inputs. When using high impedance probes,

the direct outputs may be used. Selection of outputs is via the

on board U links.

e) CALIBRATE the vector voltmeter and the leads to be used.

The calibration should be performed at the chosen baseband

frequency and level for maximum accuracy.

f) Vary the RF input frequency either side of the LO and note

the relative I and Q gain and phase reading.

If you experience any difficulties with this board, or require

further help, please contact

Robert Marsh on 01793 518234

or

Fred Herman on 01793 518423