TQ5622 Просмотр технического описания (PDF) - TriQuint Semiconductor

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TQ5622

3V PCS Receiver IC With Power- Down

TriQuint Semiconductor 

TQ5622

Data Sheet

Mixer

The mixer of the TQ5622 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 as low as

-7dBm. The 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 TQ5622

to operate at low LO drivel levels. However, the position of C3

shown in the applications circuit may effect the gain of the LO

buffer amplifier, it should be placed as close as practicable to

Pin 6.

The 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 TQ5622 LO input via a 50Ω

transmission line with no additional components.

Mixer Input

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.

Mixer IF Port

The Mixer IF output is an "open-drain" configuration, allowing

flexibility in matching to various filter types and various IF

frequencies.

For evaluation of the LNA and mixer, it is usually necessary to

impedance match the IF port to the 50Ω test system. When

verifying or adjusting the matching circuit on the prototype circuit

board, the LO drive should be injected at pin 5 at the nominal

power level of -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 ceramic IF filter. The mixer supply

voltage is applied through the IF port, so the matching circuit

topology must contain either an RF choke or shunt inductor. An

extra DC blocking capacitor is not necessary if the output will be

attached directly to a SAW or ceramic bandpass filter.

Figure 3 illustrates a shunt L, series C, shunt C IF matching

network. It is one of the simplest matching networks and

requires the fewest components. DC current can be easily

injected through the shunt inductor and the series C provides a

DC block, if needed. The shunt C, is used to reduce the LO

leakage.

Pin 11

Pin 10

1000pF

10 pF

100nH

IF out

15pF

V IF

Figure 3, IF Output Match, 135 MHz

Power down, “sleep” mode

The power down circuit is used to reduce average power

consumption of the receiver in TDMA applications by toggling

the receiver on and off within the TDMA receive time slot when

no signal is present. The power down circuitry operates through

6

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

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