TQ5121 View Datasheet(PDF) - TriQuint Semiconductor

Part Name

Description

Manufacturer

TQ5121

3V Cellular TDMA/AMPS LNA/mixer Receiver IC

TriQuint Semiconductor 

Fig 4. LO Spurious Response Diagram

TQ5121

Mixer

RF

IF

50 W

LO

Spectrum

Analyzer

SIG 1:

flo

Directional

+ Coupler

SIG 2:

flo +/- IF

Table 3. LO Spurious Response Data

LO/Spurious Mixer LO Port

C/V

(MHz)

Input Power

(dB)

991/1101

-57

-71.7

991/1101

-58.9

-71.8

Calculation of Nominal L Value

The node between the LO buffer amplifier and the mixer FET is

brought out to Pin 3 (L_tune) and connected to a shunt inductor

to AC ground. This inductor is selected to resonate with internal

capacitance at the LO frequency in order to suppress out-of-

band gain and improve noise performance.

The internal capacitance of the LO amplifier output plus the

stray capacitance on the board surrounding Pin 3 is

approximately 1.8 pF. The inductor is selected to resonate with

the total capacitance at the LO frequency using the following

equation:

L=

1

C(2Π

f

)2

,

where

⋅C

=

1.5 pF

Must be confirmed with measurements on a board

approximating the final layout.

TQ5121

Data Sheet

Measuring the LO Frequency Response

The frequency response of the LO driver amplifier can be

measured using a semi-rigid probe (see Fig. 5) and a network

analyzer.

Connect port 1 to the LO input (Pin 4) of the TQ5121 with the

source power set to deliver -7 dBm. Connect the coaxial probe

to Port 2 and place the probe tip approximately 0.1 inch away

from either Pin 3 or the inductor.

Fig 5. LO Buffer Frequency

Response

Network

Analyzer

Port 1 Port 2

Probe

3

4

TQ5121

-30

-32

-34

-36

-38

-40

-42

700 800 900 1000 1100 1200

Frequency (MHz)

If the calculated shunt inductor (L2) is not a standard value, the

AC ground, implemented with C3, can be slide along the

transmission line to adjust for the right inductance (fig 6). Once

this is completed, the peak of the response should be centered

at the center of the LO frequency band.

Fig 6. Adjusting the

AC Ground

Ground

3

Placement of inductor

will adjust between

standard values

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

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