Preliminary
7-20
RF2713
Rev A2 010129
5
Pin
Function
Description (Demodulator Configuration)
Interface Schematic
1I INPUT A
When the RF2713 is configured as a Quadrature Demodulator, both
mixers are driven by the IF. Whether driving the mixers single-endedly
(as shown in the application schematic) or differentially, the A Inputs
(pins 1 and 3) should be connected to each other. Likewise, both B
Inputs (pins 2 and 4) should be connected to each other. This ensures
that the IF will reach each mixer with the same amplitude and phase,
yielding the best I and Q output amplitude and quadrature balance.
Note that connecting the inputs in parallel changes the input imped-
ance (see the Gilbert Cell mixer equivalent circuit). The single-ended
input impedance (as shown in the application circuit) becomes 630
Ω,
but in the balanced configuration, the input impedance would remain
1260
Ω.
The mixers are Gilbert Cell designs with balanced inputs. The equiva-
lent schematic for one of the mixers is shown on the following page.
The input impedance of each pin is determined by the 1260
Ω resistor
to VCC in parallel with a transistor base. Note from the schematic that
all four input pins have an internally set DC bias. For this reason, all
four inputs (pins 1 through 4) should be DC blocked. The capacitance
values of the blocking capacitors is determined by the IF frequency.
When driving single-endedly, both the series (pins 1 and 3) and shunt
(pins 2 and 4) blocking capacitors should be low impedances, relative
to the 630
Ω input impedance.
2I INPUT B
Same as pin 1, except complementary input.
See pin 1.
3Q INPUT A
Same as pin 1, except Q Buffer Amplifier.
See pin 1.
4Q INPUT B
Same as pin 3, except complementary input.
See pin 1.
5BG OUT
Band Gap voltage reference output. This voltage output is held con-
stant over variations in supply voltage and operating temperature and
may be used as a reference for other external circuitry. This pin should
not be loaded such that the sourced current exceeds 1mA. This pin
should be bypassed with a large (0.1
µF) capacitor.
6
I IF OUT
This pin is not used in the Demodulator Configuration, but must be con-
nected to VCC in order to properly bias the I mixer.
7
Q IF OUT
Same as pin 6, except Q mixer.
Same as pin 6.
8Q OUT
Q Mixer’s Baseband Output. This pin is NOT internally DC blocked and
has DC present due to internal biasing. This is an emitter-follower type
output with an internal 2k
Ω pull-down resistor. Even though the AC out-
put impedance is ~50
Ω, this pin is intended to drive only high imped-
ance loads such as an opamp or an ADC. The output transistor is NOT
biased such that it can drive a large signal into a 50
Ω load. DC cou-
pling of this output is permitted provided that the DC impedance to
ground, which appears in parallel with the internal pull-down resistor, is
significantly greater than 2k
Ω.
9I OUT
Same as pin 8, except Q Mixer’s Baseband Output.
Same as pin 8.
10
GND
Ground connection. Keep traces physically short and connect immedi-
ately to ground plane for best performance.
11
GND
Same as pin 10.
12
GND
Same as pin 10.
1260
Ω
1260
Ω
INPUT A
V
CC
V
CC
INPUT B
IF OUT
I/Q OUT
2k
Ω
V
CC
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