MGCM02
Data Sheet
RSSI
Output
(V)
VDD/2
Input Signal (dBm)
Figure 6 - RSSI Characteristic
The I+,Q+ outputs are switched high and the I-,Q-
outputs are switched low to set the IQ modulator in a
transmit device such as the Zarlink MGCT04 into FM
mode. When using the MGCT04 the transmit IF VCO
will be operating at twice the IF frequency. The
frequency deviation therefore required on the VCO
will be twice that required at the transmit output of
that device.
Transmit
TDMA IS136 Mode I/Q Modulation
The inputs to MGCM02 are derived from baseband
digital to analog converters. These signals are
passed through variable gain buffers. The gain of
these buffers can be programmed from 0 to 12 dB in
3 dB increments allowing compatibility with a number
of baseband and transmit modulator devices.
The input to the MGCM02 can be programmed to be
either differential or single ended using the I channel
inputs and the Q channel inputs are powered down.
The differential input mode is the same as for TDMA.
In the single ended mode only the TXI+ input is
active and the FM signal must be capacitively
coupled into this pin. This mode would only be used
where the FM signal is from a different source to the
I channel. When using this mode the differential I
outputs from a baseband device must be in high
impedance state.
The buffers are followed by reconstruction filters to
remove spurious responses from preceding digital to
analog converters. These filters are third order
Butterworth with 25kHz cut off. The filters contain
automatic calibration to set the cut off frequency.
This can be controlled via the serial programming
bus.
All inputs and outputs are differential
The transmit filtering used for FM mode is the same
as for TDMA mode.
AMPS FM mode
Synthesisers and VCO
There is
a
choice of modes available to
accommodate the modulation technique used and
different baseband interfaces.
Two VHF PLL synthsisers are included for the
generation of receive and transmit IF LO signals. The
two synthesisers are identical.
If I,Q modulation is used for FM modulation then the
same mode is used as for TDMA ie differential input
and differential output on the I and Q channels.
The input to the receive PLL is from the on chip VCO.
This operates at twice the LO frequency. An external
tank circuit is required - typically a parallel capacitor
and inductor with a varactor for tuning.
If direct modulation of the transmit IF VCO is used
then the TX FM (E5) single-ended output is used.
12
ZARLINK [ ZARLINK SEMICONDUCTOR INC ]
