Low-Voltage, Phase-Reversal

Analog Switch

8

_______________________________________________________________________________________

Bipolar Supplies

The MAX4528 operates with bipolar supplies between

±2.7V and ±6.0V. The V+ and V- supplies need not be

symmetrical, but their sum cannot exceed the 13V

absolute maximum rating (see

Absolute Maximum

Ratings).

Single Supply

The MAX4528 operates from a single +2.7V to +12V

supply when V- is connected to GND. Observe all of

the bipolar precautions when operating from a single

supply.

__________Applications Information

The MAX4528 is designed for DC and low-frequency-

signal phase-reversal applications. Both DC and AC

symmetry are optimized for use with ±5V supplies.

Signal Phase/Polarity Reversal

The MAX4528 can reverse the phase or polarity of a

pair of signals that are out-of-phase and balanced to

ground. This is done by routing signals through the

MAX4528 and, under control of IN, reversing the two

signals paths inside the switch before sending out to a

balanced output. Figure 1 shows a typical example.

The MAX4528 cannot reverse the phase or polarity

of a single grounded signal, as can be done with an

inverting op amp or transformer.

Balanced Modulator/Demodulator

The MAX4528 can be used as a balanced modulator/

demodulator at carrier frequencies up to 100kHz

(Figure 2). Higher frequencies are possible, but as fre-

quency increases, small imbalances in the MAX4528’s

internal capacitance and resistance gradually impair

performance. Similarly, imbalances in external circuit

capacitance and resistance to GND reduce overall car-

rier suppression.

The carrier is applied as a logic-level square wave to

IN. (Note that this voltage can go as negative as V-.)

For best carrier suppression, the power-supply volt-

ages should be equal, the square wave should have a

precise 50% duty cycle, and both the input and output

signals should be symmetrical around ground. Bypass

V+ and V- to GND with 0.1µF ceramic capacitors, as

close to the IC pins as possible. In critical applications,

carrier suppression can be optimized by trimming duty

cycle, DC bias around GND, or external source and

load capacitance.

In signal lines, balancing both capacitance and resis-

tance to GND produces the best carrier suppression.

Transformer coupling of input and output signals

provides the best isolation and carrier suppression.

Transformers can also provide signal filtering, imped-

ance matching, or low-noise voltage gain. Use a

center-tapped transformer or high-resistance voltage

divider to provide a DC path to GND on either the input

or output signal. This ensures a DC path to GND and

symmetrical operation of the internal switches.

Y

IN

LOGIC LOW

GND

X

B

A

MAX4528

MAX4528

TRUTH TABLE

IN

O

1

A

Y

X

B

X

Y

V-

INPUTS

V+

V+

V-

OUTPUTS

Y

IN

LOGIC HIGH

X

B

A

GND

V-

V-

INPUTS

V+

V+

OUTPUTS

Figure 1. Typical Application Circuits