SA620 datasheet(4/11 Pages) PHILIPS

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Philips Semiconductors RF Communications Products

Product specification

SA620

Low voltage LNA, mixer and VCO — 1GHz

December 15, 1993

Figure 1. A Complete LNA, Mixer and VCO

LNA ENABLE

LNA GND

LNA IN

LNA GND

MIXER PD

OSC PD

OSC1

OSC2

Vcc

LNA GND

LNA OUT

LNA BIAS

MIXER IN

MIXER GND

MIXER BYPASS

MIXER OUT

OSC GND

VCO OUT

LNA IN

C23

C22

56nH

1.8pF

2.7nH

3.3pF

SMV 1204 - 099

Alpha Industries

GND

100pF

C19

100pF

C18

2.2pF

LNA OUT

C17

100pF

MIXER IN

C16

5.6pF

C14

1-5pF

R = 9k x (VCC – 1)

VCC

C20

100pF

C21

C13

12pF

150nH

C15

C12

10pF

MIXER OUT

L = 260 mils

w = 15 mils

VCO OUT

100pF

C10

100pF

VCC

µF

0.44

µF/(VCC–1)

0.1

µF

0.1

µF

100pF

0.1

µF

0.1

µF

(50

Ω)

V_CONTROL

(0 to VCC)

VCC

SA620

VCC

LNA ENABLE

Ω

(1k

Ω, 83MHz)

10k

Ω

10k

Ω

L = 260 mils

w = 15 mils

2.7nH

3.9pF

4.7nH

535 mils

4.7nH

535 mils

4.7nH

535 mils

4.7nH

535 mils

L = 160 mils

w = 15 mils

C11

1000pF

Ω

MIXER OUT

(50

Ω, 83MHz)

CIRCUIT TECHNOLOGY

LNA

Impedance Match: Intrinsic return loss at the

input and output ports is 7dB and 9dB,

respectively. With no external matching, the

associated LNA gain is

≈10dB and the noise

figure is

≈1.4dB. However, the return loss

can be improved at 900MHz using suggested

L/C elements (Figure NO TAG) as the LNA is

unconditionally stable.

Noise Match: The LNA achieves 1.6dB

noise figure at 900MHz when S11 = -10dB.

Further improvements in S11 will slightly

increase the NF and S21.

Thru-Mode: A series switch can be activated

to feed RF signals from LNA input to output

with an attenuator (S21 = –7.5dB). As a

result, the power handling is greatly improved

and current consumption is decreased by

3.2mA as well. However, if this mode is not

required, C23 and R6 can be deleted.

Temperature Compensation: The LNA has

a built-in temperature compensation scheme

to reduce the gain drift to 0.003dB/

°C from

–40

°C to +85°C.

Supply Voltage Compensation: Unique

circuitry provides gain stabilization over wide

supply voltage range. The gain changes no

more than 0.5dB when VCC increases from

3V to 5V.

Mixer

Input Match: The mixer is configured for

maximum gain and best noise figure. The

user needs to supply L/C elements to

achieve this performance.

Mixer Bypass: To optimize the IP3 of the

mixer input, one must adjust the value of C14

for the given board layout. The value

typically lies between 1 and 5pF. Once a

value if selected, a fixed capacitor can be

used. Further improvements in mixer IP3 can

be achieved by inserting a resistive loss at

the mixer input, at the expense of system

gain and noise figure.

Tracking Bandpass Filter: At the LO input

port of the mixer there is a second-order

bandpass filter (approx. 50MHz bandwidth)

which will track the VCO center frequency.

The result is the elimination of low frequency

noise injected into the mixer LO port without

the need for an external LO filter.

Power Down: The mixer can be disabled by

connecting Pin 7 to ground. If a Schottky

diode is connected between Pin 1 (cathode)

and Pin 7 (anode), the LNA disable signal will

control both LNA and mixer simultaneously

When the mixer is disabled, 3mA is saved.

Test Port: Resistor R5 can be substituted

with an external test port of 50

Ω input

impedance. Since R5 and MIXER OUT have

the same output power, the result is a direct

power gain measurement.

VCO

Automatic Leveling Loop: An on-chip

detector and loop amplifier will adjust VCO

bias current to regulate the VCO amplitude

regardless of the Q-factor (>10) of the

resonator and varactor diode. However, the

real current reduction will not occur until the

VCO frequency falls below 500MHz. For a

typical resonator the steady-state current is

3mA at 800MHz.

Buffered VCO Output: The VCO OUT (Pin

11) signal can drive an external prescaler

directly (see also the Philips SA7025 low

voltage, fractional-N synthesizer). The

extracted signal levels need to be limited to

–16dBm or less to maintain mixer IIP3.

Phase Noise: If close-in phase noise is not

critical, or if an external synthesizer is used,

C4 (Pin 8) can be decreased to a lower

value.

Power-Down: The VCO can be disabled by

connecting Pin 8 to ground. If a Schottky

diode is connected between Pin 1 (cathode)

and Pin 8 (anode), the LNA disable signal will

control both LNA and VCO simultaneously.

When the VCO is disabled, 3mA is saved.

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