AD8519/AD8529

Rev. D | Page 13 of 16

10× MICROPHONE PREAMP MEETS PC99

SPECIFICATIONS

This circuit, while lacking a unique topology, is anything but

featureless when an AD8519 is used as the op amp. This preamp

gives 20 dB gain over a frequency range of 20 Hz to 20 kHz and

is fully PC99 compliant in all parameters including THD + N,

dynamic range, frequency range, amplitude range, and crosstalk.

Not only does this preamp comply with the PC99 specifications,

it far surpasses them. In fact, when the input noise is 120 dB,

able for most professional 20-bit audio systems. At 120 dB THD

+ N in unity gain, the AD8519 is suitable for 24-bit professional

audio systems. In other words, the AD8519 will not be the

limiting performance factor in audio systems despite its small

size and low cost.

Slew rate related distortion is not present at the lower voltages

because the AD8519 is so fast at 2.1 V/μs. A general rule of

thumb for determining the necessary slew rate for an audio

system is to take the maximum output voltage range of the

device, given the design’s power rails, and divide by two. In

Figure 24, the power rails are 2.7 V and the output is rail-to-rail.

Enter these numbers into the equation: 2.7/2 = 1.35 V, and the

minimum ideal slew rate is 1.35 V/μs.

While this data sheet gives only one audio example, many audio

circuits are enhanced with the use of the AD8519. Examples

include: active audio filters such as bass, treble, and equalizers;

PWM filters at the output of audio DACs; buffers and summers

for mixing stations; and gain stages for volume control.

1kΩ

AD8519

2.7V

30.9kΩ

2.7V

3.09kΩ

46.4kΩ

93.1kΩ

2.7V

240pF

48kΩ

CODEC LINE IN

OR MIC IN

10µF ELECT

MIC

IN

1nF

NPO

C1

1µF

Figure 24. 10× Microphone Preamplifier

TWO-ELEMENT VARYING BRIDGE AMPLIFIER

There are a host of bridge configurations available to designers.

For a complete analysis, look at the ubiquitous bridge and its

different forms. Refer to the 1992 Amplifier Applications Guide1.

Figure 25 is a schematic of a two-element varying bridge. This

configuration is commonly found in pressure and flow transduc-

ers. With a two-element varying bridge, the signal is 2× as

compared to a single-element varying bridge. The advantages

of this type of bridge are gain setting range and single-supply

application. Negative characteristics are nonlinear operation

and required R matching. Given these sets of conditions,

requirements, and characteristics, the AD8519 can be successfully

used in this configuration because of its rail-to-rail output and

low offset. Perhaps the greatest benefits of the AD8519, when

used in the bridge configuration, are the advantages it can bring

when placed in a remote bridge sensor. For example, the tiny

SC70 and SOT-23 packages reduce the overall sensor size; low

power allows for remote powering via batteries or solar cells,

high output current drive to drive a long cable; and 2.7 V

operation for two-cell operation.

R

R

R

R

AD8519

2.7V

Figure 25. Two-Element Varying Bridge Amplifier