TQ5M34
Data Sheet
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13
Here is an approximate equation for Rgic as a function of IF
stage Idd: Rgic ~ 0.6 / IDD_IF
Remember that due to the filter-mxer interaction, the final
Rgic may need to be changed to optimze performance once
LO power is applied.
GIC PIN
GIC PIN
Chip
GND
Chip
GND
0 to 5 ohms
20 to 60 ohms
20 to 60 ohms
sets IF
current
Zc bypass
at IF Freq
Zc bypass
at IF Freq
AC degen
sets IF
current
Figure 6: Two Recommended GIC Networks
IF Match Design:
The Mxer IF output (Pin 2) is an "open-drain" configuration,
allowing for flexibility in efficient matching to various filter
types and at various IF frequencies. An optimumlumped-
element-matching network must be designed for maximum
TQ5M34 conversion gain and mnimummatching network
loss.
When designing the IF output matching circuit, one has to
consider the output impedance (pin 3) of the IF Amplifier. It
will vary somewhat depending on the quiescent current and
the LO drive. The IF frequency can be tuned from45 to 400
MHz by varying component values of the IF output matching
circuit. The IF output pin also provides the DC bias for the
output FET.
In the user's application, the IF output is most commonly
connected to a narrow band SAW or crystal filter with
impedance from500 -1000
with 1 - 2 pF of capacitance. A
conjugate match to a higher filter impedance is generally less
sensitive than matching to 50
. When verifying or adjusting
the matching circuit on the prototype circuit board, the LO
drive should be injected at the nomnal power level (-4 dBm,
since the LO level does have an impact on the IF port
impedance.
There are several networks that can be used to properly
match the IF port to the SAW or crystal IF filter. The IF FET
current is applied through the IF output Pin 2, so the matching
circuit topology must contain either an RF choke or shunt
inductor.