SSM2220 Data Sheet
Rev. C | Page 8 of 12
APPLICATIONS INFORMATION
5V
A
V
= 10
C
F
= 30pF
20µs
PULSE RESPONSE
A
V
= 1000
V
ERT
= 1nV/DIV
LOW FREQUENCY NOISE
10µF
AD8671
2
3
6
7
4
0.01µF
0.01µF
–15V
+15V
V
OUT
Q5 Q2Q3
Q7
Q4Q1
Q6
+ –
83Ω
1.5kΩ
0.01%
1.5kΩ
0.01%
27kΩ
–15V
RED
LED
+15V
–15V
+
0.001µF
SSM2220 PAIRS:
Q1 – Q2
Q3 – Q4
Q5 – Q6
150Ω
0.01µF
+
10µF 0.001µF
03096-016
Figure 16. Super Low Noise Amplifier
SUPER LOW NOISE AMPLIFIER
The circuit in Figure 16 is a super low noise amplifier, with equiv-
alent input voltage noise of 0.32 nV/√Hz. By paralleling SSM2220
matched pairs, a reduction of the base spreading resistance by a
factor of 3 results in a further reduction of amplifier noise by a fac-
tor of √3. Additionally, the shot noise contribution is reduced by
maintaining a high collector current (2 mA/device), which reduces
the dynamic emitter resistance and decreases voltage noise. The
voltage noise is inversely proportional to the square root of the
stage current, whereas current noise increases proportionally.
Accordingly, this amplifier capitalizes on voltage noise reduction
techniques at the expense of increasing the current noise. However,
high current noise is not usually important when dealing with
low impedance sources.
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 17).
0.1
0.001
0.01
10
100k
10k1k100
TOTAL HARMONIC DISTORTION (%)
FREQUENCY (Hz)
600Ω LOAD
NO LOAD
03096-017
Figure 17. Total Harmonic Distortion vs. Frequency of Circuit in Figure 16
