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TQ9223C

3V Cellular TDMA/AMPS LNA/mixer Receiver IC

TriQuint Semiconductor 

TQ9223C

Data Sheet

A number of inductor/capacitor values can be selected that will

effectively transform the LNA output impedance to the system

impedance. The actual values selected will be governed by the

trade-off between optimum impedance match and maximum IP3

match.

Mixer RF Input (Pin 11)

The mixer RF input is matched close to 50 ohms and is

internally DC-blocked. Pin 11 may be directly connected to the

filter output. The filter must be as close as possible to the mixer

RF input to maintain the proper termination impedance at the

LO frequency. Include a shunt inductor of 33nH at the mixer RF

input to improve the mixer noise performance by providing a

short to ground at the IF frequency. This provides a secondary

benefit of slightly improved input match.

Mixer LO Input (Pin 1)

The mixer LO input is matched close to 50 ohms and is

internally DC-blocked. Pin 1 may be directly connected to the

LO input signal. A level greater than –6dBm is recommended.

Standard VCO outputs of –2dBm work well.

LO Tuning (Pin 13)

A shunt L on pin 13 resonates with some internal capacitance to

produce a bandpass frequency response of the LO buffer

amplifier. This attenuates noise at +/- one IF frequency away

from the LO frequency. The approximate value of L is

determined by the following equation:

L=1/C (2πf)2, where C=2.2pF

In practice, the value (and/or placement) of L should be

empirically determined for a particular layout, since stray

capacitance on the PCB layout can move the resident frequency

from the expected ideal. The actual value of L should be

adjusted until the buffer response (pin 1-> pin 13) produces a

peak at the LO frequency. A measurement of the response may

be accomplished with a simple coaxial probe “sniffer,”in which

the end is positioned 50 – 100 mils from the inductor at pin 13.

The frequency response of the LO buffer amplifier (pin 13) is

directly measured on the network analyzer as the LO input (pin

1) is swept in frequency. The LO drive level should be set at

approximately the operating level (-6 to -3dBm) for this

measurement. This “tuning”needs to be done only in design,

not in production.

Mixer IF Interfacing

The mixer IF port is a high-impedance, open-drain output. The

impedance is a few K ohms in parallel with less than 1pF

capacitance. The IF port S-parameters (S11) are listed in the

table over the frequency range of 45MHz to 250MHz. It is

possible to use IFs above and below this range: however, at low

frequencies the noise increases, and at high frequencies the

LO/IF, RF/IF isolation decreases.

The open-drain output permits matching to any chosen filter

impedance. In general, a conjugate impedance match is

recommended on this port to achieve best power gain, noise

figure and output 3rd-order intercept. It is also important to

properly center the tuned circuit at the desired IF. This

maximizes circuit robustness to component tolerances. For

proper mixer operation, pin 14, the open-drain output, must also

be biased to Vdd. A practical matching network, which includes

biasing, is shown.

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For additional information and latest specifications, see our website: www.triquint.com

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