Philips Semiconductors | Application note | |
|
|
|
Using the NE/SA5234 amplifier | AN1651 | |
|
|
|
* 4 | ) | + | 68dB | (EQ. 5.) | ||
S N | 20log10 (1.0 4x10 |
|
|
|
SN 20 log |
| 100x10* 3 | (EQ. 7.) | |
10 |
| |||
| 1.6x10* 4 |
|
|
+56dB
A 56dB S/N will provide superior voice channel communications .
This is quite adequate for good quality audio applications.
Next assume that the bandwidth is cut to 3.0kHz with an input of
1mVRMS. The RMS noise is modified by the ratio of the root of the noise channel bandwidths.
| 3x103 |
|
| |
| @ EN + 1.6VRMS | (EQ. 6.) | ||
|
|
| ||
| ||||
| 20x103 |
|
|
Amplified Noise = 160μVRMS
| en 1.6μV |
| |
| 100kΩ | en | |
1mVRMS | + | + | |
± | ± | ||
| |||
| RS = 100Ω |
| |
| x100 |
|
x10
1mVRMS SIGNAL +1.6mVRMS NOISE
SL00636
Figure 8.
10k |
| + | VCC |
1μF |
|
|
|
| 100k |
| UNITY GAIN |
|
|
| VCC |
| 3 + |
| 2 |
|
| 1 | |
2.2μF | 2 ± |
|
|
600Ω |
|
|
|
|
|
| RL = 600Ω |
1μF |
|
|
|
10k | 10k | + VCC | |
|
|
|
|
|
| VCC |
|
ST1700 |
|
|
| 2 |
|
| 3 | + | 1 | 4.7μF |
|
1μF | 2 | ± |
|
|
|
|
|
|
|
| |
600Ω | 1k |
|
| 10k | 100pF |
40dB CIRCUIT |
|
|
|
|
ST1700
DISTORTION
ANALYZER
SL00637
Figure 9. NE5234 THD Test Circuits
VI. MULTIPLE STAGE CONSIDERATIONS
Since multiple noise generators are
This makes
For this reason it is good practice to make the preamp stage gain as high as practical to boost signal levels to the second stage allowing at least an
instance, a signal input which exceeds the input noise of the following stage by a factor of 10:1 will only be degraded by 0.5% or
The Second stage output noise is:
1991 Oct | 6 |