NE570(2003) Ver la hoja de datos (PDF) - Philips Electronics
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NE570 Datasheet PDF : 12 Pages
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Philips Semiconductors
Compandor
Product data
NE570
which means our overall offsets are typically about mV. The
distortion is not affected by the magnitude of the gain control
current, and it does not increase as the gain is changed. This
second harmonic distortion could be eliminated by making perfect
transistors, but since that would be difficult, we have had to resort to
other methods. A trim pin has been provided to allow trimming of the
internal offsets to zero, which effectively eliminated second
harmonic distortion. Figure 15 shows the simple trim network
required.
4
VOS = 5 mV
3
4 mV
2
3 mV
2 mv
1
1 mV
0.34
–6
0
+6
INPUT LEVEL (dBm)
SR00688
Figure 14. ∆G Cell distortion versus offset voltage
VCC
6.2 kΩ
To THD Trim
≈200 pF
R
3.6 V
20 kΩ
SR00689
Figure 15. THD Trim network
Figure 16 shows the noise performance of the ∆G cell. The maximum
output level before clipping occurs in the gain cell is plotted along
with the output noise in a 20 kHz bandwidth. Note that the noise
drops as the gain is reduced for the first 20 dB of gain reduction.
At high gains, the signal to noise ratio is 90 dB, and the total
dynamic range from maximum signal to minimum noise is 110 dB.
+20
0
–20
110 dB
–40
MAXIMUM
SIGNAL LEVEL
90 dB
–60
–80
–100
–40
–20
VCA GAIN (dB)
NOISE IN
20 kHz BW
0
SR00690
Figure 16. Dynamic range
Control signal feedthrough is generated in the gain cell by imperfect
device matching and mismatches in the current sources, I1 and I2.
When no input signal is present, changing IG will cause a small
output signal. The distortion trim is effective in nulling out any control
signal feedthrough, but in general, the null for minimum feedthrough
will be different than the null in distortion. The control signal
feedthrough can be trimmed independently of distortion by tying a
current source to the ∆G input pin. This effectively trims I1. Figure 17
shows such a trim network.
VCC
R-SELECT FOR
100 kΩ
3.6 V
470 kΩ
TO PIN 3 OR 14
SR00691
Figure 17. Control signal feedthrough
2003 Apr 03
8
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