TSA5059TS datasheet(16/24 Pages) PHILIPS

16 / 24 page

1999 Oct 05

Philips Semiconductors

Preliminary speciﬁcation

2.7 GHz I2C-bus controlled low phase

noise frequency synthesizer

TSA5059

handbook, full pagewidth

TSA5059

FCE124

1.2 k

Ω

18 pF

4 MHz

TSA5059

1.0 nF

Fig.5 Application for using one crystal with two TSA5059s.

I2C-bus crosstalk and loop ampliﬁer

The TSA5059 includes a loop amplifier between pin CP

and pin VT. While this amplifier shares the same ground

pin as the I2C-bus, there may be some I2C-bus crosstalk.

The best way to avoid any I2C-bus crosstalk, both in the

PLL IC and in the application (i.e. parasitic coupling

between the I2C-bus lines and the VCO coil), is to avoid

the I2C-bus signal to come in the RF part by using an

I2C-bus gate that allows only the messages for the PLL to

go to the PLL, and to avoid unnecessary repeated

sending. Such a gate is integrated in most of the Philips

digital demodulators.

If I2C-bus crosstalk is still a problem, it is possible not to

use the internal amplifier, and to replace it with a NMOS

transistor in the application as given in Fig.6. In this case

the pin VT is left open, and it is possible to implement on

the PCB the foot print for a jumper between the tuning

voltage line and pin VT to be able to choose either the

internal amplifier (mounting the jumper and not the NMOS

transistor) or the external amplifier (mounting the NMOS

transistor and not the jumper). It is recommended to use a

BSH111 or BSH121 N-channel MOS transistor. The

threshold voltage of the transistor has to be lower than

2.0 V.

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