MGCM02
Data Sheet
The programming will be described in more detail in
the following sections. Serial bus timing is shown in
figure 5.
CONT<2> sets the bandwidth of the 60 kHz
bandpass filter. The low bandwidth mode (CONT<2>
= 1) should be used for FM mode however the higher
bandwidth mode (+/-20 kHz) may be used in TDMA
operation.
Receive Programming
The FM gain control CONT<3> is inactive unless
RSS <0> is set to 1 as described in the next section.
MGCM02 has two basic receive modes:
1. I/Q mode. The 60 kHz IF signal is mixed down to
baseband I and Q signals. This mode is used for
IS136 TDMA and may also be used for AMPS.
CONT<2> sets the bandwidth of the 60 kHz
bandpass filter. The low bandwidth mode (CONT<2>
= 1) should be used for FM mode however the higher
bandwidth mode (+/-20 kHz) may be used in TDMA
operation.
2. FM mode. The baseband I/Q path is powered
down and the MGCM02 discriminator is used for
demodulation. This mode can be used for
AMPS.
RSS allows manual control of the input attenuator in
conjunction with CONT<3>.
These modes are selected by the RX mode bit -
Word 7, Bit 11
RSS
Operation
0
1
Normal FM Mode
RX
Mode
Manual 32 dB Gain Enable
0
1
I / Q
FM
LOI - Word 7 bit 3 - is used to select high side or low
side LO injection for the downconverter to 60kHz.
The internal 60 kHz I and Q signals are also
reversed to take account of this and enable the
image rejection to operate correctly.
Additional control is provided by the receive control
bits - Word 7 Bits 9:6. These program MGCM02 gain
in I and Q mode and allow the input attenuator to be
manually controlled.
LOI
Operation
CONT <3:0>
Mode
0
1
High side LO
Low side LO
X
X
X
X
X
X
0
X
X
X
X
0
0
0
0
1
Gain +0dB
Gain +12dB
Extra post discriminator filtering can be programmed
using LPC<1:0> and PDF<1:0> - Word 8 Bits 15-12.
The PDF bits connect the switched capacitor
baseband filters after the FM discriminator and are
used to improve the discriminator output
performance. The LPF bits allow the cut-off
frequency to be reduced to 25 kHz. The LPC and
PDF bits should only be used in FM mode. In TDMA
mode they should be set to zero.
1
0
Gain +15dB
1
1
Gain +18dB
X
X
X
X
X
X
X
X
+/- 20kHz Bandwidth
+/- 16kHz Bandwidth
FM Low Gain
1
X
X
1
FM High Gain
Normally the standard gain setting of CONT<1:0> =
00 should be used. The extra gain is provided in the
amplifier after the bandpass filter and the low pass
baseband filter.
14
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