EUA2011 datasheet(11/16 Pages) EUTECH

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EUA2011

DS2011 Ver 1.1 Dec. 2007

Application Information

Fully Differential Amplifier

The EUA2011 is a fully differential amplifier with

differential inputs and outputs. The fully differential

amplifier consists of a differential amplifier and a

common-mode amplifier. The differential amplifier

ensures that the amplifier outputs a differential voltage on

the output that is equal to the differential input times the

gain. The common-mode feedback ensures that the

common-mode voltage at the output is biased around

VDD/2 regardless of the common-mode voltage at the

input. The fully differential EUA2011 can still be used

with a single-ended input; however, the EUA2011

should be used with differential inputs when in a noisy

environment, like a wireless handset, to ensure maximum

noise rejection.

Advantages of Fully Differential Amplifiers

Input-coupling capacitors not required:

- The fully differential amplifier allows the inputs to

be biased at voltage other than mid-supply. For

example, if a codec has a midsupply lower than the

midsupply of the EUA2011, the common-mode

feedback circuit will adjust, and the EUA2011 outputs

will still be biased at midsupply of the EUA2011. The

inputs of the EUA2011 can be biased from 0.5V to

VDD – 0.8 V. If the inputs are biased outside of that

range, input-coupling capacitors are required.

Midsupply bypass capacitor, C(BYPASS), not required:

- The fully differential amplifier does not require a

bypass capacitor. This is because any shift in the

midsupply affects both positive and negative channels

equally and cancels at the differential output.

Better RF−immunity:

-GSM handsets save power by turning on and shutting

off the RF transmitter at a rate of 217 Hz. The

transmitted signal is picked-up on input and output

traces. The fully differential amplifier cancels the

signal much better than the typical audio amplifier.

Component Selection

Figure 30 shows the EUA2011 typical schematic with

differential inputs and Figure 31 shows the EUA2011

with differential inputs and input capacitors, and Figure

32 shows the EUA2011 with single-ended inputs.

Differential inputs should be used whenever possible

because the single-ended inputs are much more

susceptible to noise.

Table 1. Typical Component Values

REF DES

VALUE

150kΩ ( ± 0.5%)

1µF (+22%,-80%)

CI (1)

3.3nF ( ± 10%)

(1) CI is only needed for single-ended input or if VICM is

not between 0.5 V and VDD – 0.8 V. CI = 3.3 nF (with RI =

150 kΩ) gives a high-pass corner frequency of 321 Hz.

Figure 30. Typical Application Schematic with

Differential Input for a Wireless Phone

Figure 31. Typical Application Schematic with

Differential Input and Input Capacitors

Figure 32. Typical Application Schematic with

Single-Ended Input

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