TQ5122 Ver la hoja de datos (PDF) - TriQuint Semiconductor

Número de pieza

componentes Descripción

Fabricante

TQ5122

3V Cellular TDMA/AMPS Receiver IC With Power-Down

TriQuint Semiconductor 

TQ5122

Data Sheet

Mixer

The mixer of the TQ5122 uses a common source depletion

mode MESFET. The mixer is designed to operate on supply

voltages from 2.7V to 5V. A 50Ω matched on-chip buffer

amplifier allows direct connection of the LO input to

commercially available VCO’s with output drive levels down to

-7dBm. The common-gate LO buffer provides good input match

and supplies the voltage gain needed to drive the mixer FET.

The mixer also has an "open-drain" IF output which provides

flexibility in matching to various IF frequencies and filter

impedances, see Figure 2.

LO Input

LO Bias Mixer RF

and

Input

Tuning

Open Drain

IF Output

Figure 2, Mixer Section

LO Input Port

The LO input port is matched to 50Ω. This allows the TQ5122

to operate at low LO drivel levels. However, the values and

positions of L2 and C3 shown in the applications circuit effect

the gain of the LO buffer amplifier and are important to the

proper operation of the TQ5122. See “Calculation of nominal L2

Value” below

The common gate buffer amplifier provides the voltage gain

needed to drive the gate of the mixer FET while using very little

current (approximately 1.5mA).

Because of the 50Ω input match of the buffer amplifier and the

internal DC blocking capacitor, the system VCO output can be

directly connected to the TQ5122 LO input via a 50Ω

transmission line with no additional components.

Mixer Input

Although the mixer input port is matched to 50Ω, TriQuint has

found that LO leakage through the Mixer RF input pin, can in

some cases, reflect off the SAW image reject filter and return

back to the mixer out of phase. This may cause some

degradation in conversion gain and system noise figure.

Sensitivity to the phenomena depends on the particular filter

model and the line length between the mixer input pin and the

filter. In some cases a small inductance can be added between

the filter and the mixer input to compensate. With some line

lengths and filter combinations, no inductor is necessary.

LO Buffer & Calculation of Nominal L2 Value

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

brought out to Pin 3 (V MX) and connected by an inductor to AC

ground. This inductor is selected to resonate with internal on

chip capacitance at the LO frequency in order to reduce 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 1.5 pF. The inductor is selected to resonate with

the total capacitance at the LO frequency using the following

equation:

L

=

1

C(2Πf

)2

, where ⋅ C

=

1.5 pF

The final values must be confirmed with measurements on a

board approximating the final layout. The final layout will affect

the value and position of L2 and its bypass capacitor, C3, see

Figure 5.

Network

Analyzer

Port 1 Port 2

Probe

3

4

TQ5122

-30

-32

-34

-36

-38

-40

-42

700 800 900 1000 1100 1200

Frequency (MHz)

Figure 3. LO Buffer Frequency Response

6

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

Share Link: