–8–

REV. B

MAT03

This amplifier exhibits excellent full power ac performance,

0.08% THD into a 600

Ω load, making it suitable for exacting

audio applications (see Figure 14b).

Figure 14b. Super Low Noise Amplifier—Total

Harmonic Distortion

LOW NOISE MICROPHONE PREAMPLIFIER

Figure 15 shows a microphone preamplifier that consists of a

MAT03 and a low noise op amp. The input stage operates at a

relatively high quiescent current of 2 mA per side, which reduces

the MAT03 transistor’s voltage noise. The 1/ƒ corner is less than

1 Hz. Total harmonic distortion is under 0.005% for a 10 V p-p

signal from 20 Hz to 20 kHz. The preamp gain is 100, but can be

a GaAsP LED as a reference. The difference between this voltage

a few percent) over a wide temperature range. The voltage differ-

ence, approximately 1 V, is dropped across the 250

Ω resistor

which produces a temperature stabilized emitter current.

CURRENT SOURCES

A fundamental requirement for accurate current mirrors and ac-

tive load stages is matched transistor components. Due to the

required to equalize collector current) and gain matching, the

MAT03 can be used to implement a variety of standard current

mirrors that can source current into a load such as an amplifier

stage. The advantages of current loads in amplifiers versus resis-

tors is an increase of voltage gain due to higher impedances,

larger signal range, and in many applications a wider signal

bandwidth.

Figure 16 illustrates a cascode current mirror consisting of two

MAT03 transistor pairs.

The cascode current source has a common base transistor in se-

ries with the output which causes an increase in output imped-

High frequency characteristics are improved due to a reduction

of Miller capacitance. The small-signal output impedance can

graph. Typical output impedance levels approach the perfor-

mance of a perfect current source.

Considering a typical collector current of 100

µA, we have:

1

1.0

Figure 15. Low Noise Microphone Preamplifier