Data Sheet
MGCM02
Applications Information
From
PLL
VHF RES
Loop
Filter
10k
MGCM02 requires a minimal number of external
components in a typical application. The TCXO input
should be ac coupled using 10 nF capacitor. Internal
currents in the device are set by a reference resistor
connected from pin 48 to ground. The recommended
value for this resistor is 100kΩ. External components
on the discriminator and RSSI pins control the output
characteristics of these functions. The recommended
components are shown in figures 9 and 10.
22p
tbd
22n
VHF RESB
22p
10k
Discriminator
Output
Figure 11 - External Tank Circuit
AUDIO
The MGCM02 transmit circuits are fully compatible
with transmit products from Zarlink Semiconductor
such as MGCT02 and MGCT04.
47p
130k
AUDIO FB
FM Operation in Fading Environment
100n
In a severe fading environment the FM performance
is improved by operating in the AGC mode. This
eliminates the switching transients using the fixed
gain FM mode, when the gain is switched by 32.5 dB
which can cause ringing and distortion in the
bandpass filter.
13k
Figure 9 - Discrminator Output Components
The FM agc mode can be selected by setting
VGAWD in Word 8 to '110'. The RSSI switching
should be disabled by setting CONT<3> and RSS
bits to '1'
RSSI
Output
RSSI
At low signal levels the gain should be set as for the
fixed gain FM mode (Pre-amp plus VGA = 26 dB),
and the agc loop should not be activated until the
RSSI output voItage is approximately 1.2 volts. This
maintains optimum intermodulation performance and
tolerance to 'down fades'.
27k
1.5n
RSSI FB
Figure 10 - RSSI Output Components
Fig 11 shows the external tank circuit required for the
receive VCO. These components should be mounted
as close as possible to the device. The actual
component values will be dependent on the required
operating frequency.
19
ZARLINK [ ZARLINK SEMICONDUCTOR INC ]
