5-96
RF9958
Rev B11 010720
5
Pin
Function
Description
Interface Schematic
1MODE
Selects between CDMA and FM mode. This is a digitally controlled
input. A logic “high” (
≥V
CC -0.7 VDC) selects CDMA mode. A logic “low”
(
<0.5V
DC) selects FM mode. In FM mode, this switch enables the FM
amplifier and turns off the I&Q modulator. The impedance on this pin is
30k
Ω. A DC voltage less than or equal to the maximum allowable Vcc
may be applied to this pin when no voltage is applied to the Vcc pins.
2Q SIG
Baseband input to the Q mixer. This pin is DC coupled. The DC level of
0.6V must be supplied to this pin to bias the transistor. Input imped-
ance of this pin is 50k
Ω minimum. A DC voltage less than or equal to
the maximum allowable Vcc may be applied to this pin when no voltage
is applied to the Vcc pins.
3Q REF
Reference voltage for the Q mixer. This voltage should be the same as
the DC voltage supplied to the Q SIG pin. For maximum carrier sup-
pression, DC voltage on this pin relative to the Q SIG DC voltage may
be adjusted. Input impedance of this pin is 50k
Ω minimum. A DC volt-
age less than or equal to the maximum allowable Vcc may be applied to
this pin when no voltage is applied to the Vcc pins.
See pin 2.
4I REF
Reference voltage for the I mixer. This voltage should be the same as
the DC voltage supplied to the I SIG pin. For maximum carrier suppres-
sion, DC voltage on this pin relative to the I SIG DC voltage may be
adjusted. Input impedance of this pin is 50k
Ω minimum. A DC voltage
less than or equal to the maximum allowable Vcc may be applied to this
pin when no voltage is applied to the Vcc pins.
See pin 5.
5I SIG
Baseband input to the I mixer. This pin is DC coupled. The DC level of
0.6V must be supplied to this pin to bias the transistor. Input imped-
ance of this pin is 50k
Ω minimum. A DC voltage less than or equal to
the maximum allowable Vcc may be applied to this pin when no voltage
is applied to the Vcc pins.
6
GND1
Ground connection for all baseband circuits including bandgap, AGC,
flip-flop, modulator and FM amp. Keep traces physically short and con-
nect immediately to ground plane for best performance.
7
VCC1
Supply Voltage for the LO1 flip-flop and limiting amp only. This supply is
isolated to minimize the carrier leakage. A 1nF external bypass capaci-
tor is required, and an additional 0.1
µF will be required if no other low
frequency bypass capacitors are nearby. The trace length between the
pin and the bypass capacitors should be minimized. The ground side of
the bypass capacitors should connect immediately to ground plane.
8LO1+, FM+
One half of the balanced modulator LO1 input. The other half of the
input, LO1-, is AC grounded for single-ended input applications. The
frequency on these pins is divided by a factor of 2, hence the carrier
frequency for the modulator becomes one half of the applied frequency.
The single-ended input impedance is 100
Ω (balanced is 200Ω). This
pin is NOT internally DC blocked. An external blocking capacitor (1nF
recommended) must be provided if the pin is connected to a device
with DC present. When FM mode is selected, the output of the flip-flop
divider circuit is switched to the AGC amplifier inputs and the modulator
mixers are not used. Note that the frequency deviation input here will
be reduced by a factor of two, due to the frequency divider operation.
9LO1-, FM-
One half of the balanced modulator LO1 input. In single-ended applica-
tions (100
Ω input impedance), this pin is AC grounded with a 1nF
capacitor.
See pin 8.
60 k
Ω
60 k
Ω
BIAS
MODE
8k
Ω
8k
Ω
Q SIG
Q REF
BIAS
BIAS
8k
Ω
8k
Ω
I SIG
I REF
BIAS
BIAS
100
Ω
100
Ω
LO1+, FM+
LO1-, FM-
V
CC1
V
CC1
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