CMX994 Datasheet, PDF (31/61 Pages) CML Microcircuits – Local Oscillator

Direct Conversion Receivers
CMX994/CMX994A/CMX994E
7.7
7.7.1
Rx Gain Register
Rx Gain: $16 – 8-bit write only
This register controls receiver gain control. All bits of this register are cleared to ‘0’ by a General Reset
command.
7
6
5
4
3
2
1
0
GS1
GS0
LNA
LNA
LNA
G2
G1
G0
Gain2
Gain1
Z₀
b7,6 LNA Gain Control Step: These bits control the LNA gain steps; the nominal step is 6dB however the
actual step size can be adjusted by+0.7dB, +1.4dB or +2.8dB, as shown in the table below. For
further information see section 8.1.3.
b7 b6 Function
0
0 Nominal step size of 6dB
0
1 Nominal step size + 0.7dB
1
0 Nominal step size+1.4dB
1
1 Nominal step size +2.8dB
b5,4 LNA Gain Control: These bits control the LNA gain in nominal 6dB steps, as shown in table below; see
also b7 - b6.
b5 b4 Function
0
0 LNA gain = Nominal
0
1 LNA gain = Nominal -6dB
1
0 LNA gain = Nominal -12dB
1
1 LNA gain = Nominal -18dB
b3
Sets the LNA output impedance. The LNA output impedance is approximately 100 if this bit is set
to ‘0’ and approximately 50 if this bit is set to ‘1’. If set to 50 the gain will be increased but with
an additional LNA current consumption of approximately 2mA.
b2-0 I/Q Baseband VGA Control
b2
b1
b0
VGA Level
1
1
1
VGA = -42dB
1
1
0
VGA = -36dB
1
0
1
VGA = -30dB
1
0
0
VGA = -24dB
0
1
1
VGA = -18dB
0
1
0
VGA = -12dB
0
0
1
VGA = -6dB
0
0
0
VGA = 0dB (Maximum gain)
7.7.2 Rx Gain: $E6 – 8-bit read only
This read only register mirrors the value in register $16; see section 7.7.1 for details of bit functions.
 2015 CML Microsystems Plc
Page 31 of 70
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