6

SL1710

I & Q OUTPUTS

The I and Q output stages of the SL1710 are sensitive to the

loads connected to them. To avoid degrading the output

signals resistive loads connected to these pins should always

be 1K

Ω or greater with a parallel capacitance of 15pF or less

For evaluation purposes this makes the output unsuitable

for connection to test equipment via normal coaxial cables. To

alleviate this problem the application board is fitted with

emitter follower buffer amplifiers which allow the connection of

loads as low as 50

Ω via coaxial cables without loading the

output stages of the SL1710. These buffer amplifiers can be

either connected in circuit, or bypassed by changing the

position of Links 1 and 2.

This technique may be used in a real application where the

SL1710 is used to drive and ADC via an anti-alias filter. Great

care must be taken to ensure that the loading conditions

stated above are not exceeded when designing the anti-alias

filter section. Use of an emitter follower buffer is the easiest

way to alleviate this constraint.

With the AGC voltage adjusted to 2.5 Volts apply an input

signal to the IF IN (pin 5) and monitor the Base Band output

level at the I and Q outputs. Adjust the RF input level until an

output level of 760mV pk-pk is achieved. For best

performance this level should not exceeded.

15pF

PRESCALER

OUTPUT

Vcc 2

2K

Fig.5 Maximum prescaler output load