SSM-2220 Ver la hoja de datos (PDF) - Analog Devices

Número de pieza

componentes Descripción

Fabricante

SSM-2220

Audio Dual Matched PNP Transistor

Analog Devices 

Data Sheet

+15V

LED

R1

250Ω

Q2

2N29007A

0.01µF

10µF

+

VIN

–15V

3

6

2

Q1

7

SSM2220

R6

100Ω

1

8

2

8

R5

100Ω

C1

50pF

AD8671 1

3

4

10µF

VOUT

R2

R3

R4

27kΩ 5kΩ

5kΩ

+

0.01µF

THD < 0.005% 20Hz TO 20kHz

0.5nV/ Hz

1/f CORNER < 1Hz

Figure 18. Low Noise Microphone Preamplifier

SSM2220

LOW NOISE MICROPHONE PREAMPLIFIER

Figure 18 shows a microphone preamplifier that consists of an

SSM2220 and a low noise op amp. The input stage operates at a

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

the SSM2220 transistor voltage noise. The 1/f 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

modified by varying R5 or R6 (VOUT/VIN = R5/R6 + 1). A total

input stage emitter current of 4 mA is provided by Q2. The con-

stant current in Q2 is set by using the forward voltage of a GaAsP

LED as a reference. The difference between this voltage and the

VBE of a silicon transistor is predictable and constant (to a few

percent) over a wide temperature range. The voltage difference,

approximately 1 V, is dropped across the 250 Ω resistor, which

produces a temperature stabilized emitter current.

Rev. C | Page 9 of 12

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