AN1512 Philips, AN1512 Datasheet - Page 4

• Manufacturer Part Number: AN1512
• Description: All in one NE5230
• Manufacturer: Philips

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Philips Semiconductors
the lower frequencies. This was due to influence of the transistor as
described previously.
BIAS ADJUST PIN
The NE5230 has another feature: the bias adjust pin. This pin is
intended to control the power supply current. The power supply
current is controlled by decreasing the internal bias current of the op
amp. When the bias current is decreased, the transconductance
(g
bandwidth. In addition, this pin can be used to turn the op amp on or
off. If the voltage at the bias adjust pin is moved to 50mV above the
voltage at the V
op amp, for all intents and purposes, is off. If, on the other hand, the
bias adjust pin is moved to 50mV below the voltage at the V
the bandwidth and slew rate are increased. The user should
exercise care when doing this.
Utilized as a frequency-controlling element, this pin can be
employed as a filter for upper band suppression. By carefully
selecting the value, a single resistor connected to the +V
be used to determine the upper cutoff frequency of this filter. Values
below 1.0M should not be used because the total power
approximately 100k . This is an unconventional way to use this pin
and this method of using the pin is not characterized. The user is
cautioned to use care when employing the pin as outlined. The
portion of supply current is too low for useful operation. The drive
capability of the output is limited to the band which lends itself to this
use is approximately the top half of the audio range. Below and
beyond that range some problems become apparent. For the lower
frequencies, the amplifier is operating far below its designed
operating values and is not optimum in its performance. See Figure
limited. The common-mode rejection ratio, power supply rejection
ratio, as well as the input parameters go out of the data sheet-
specified values at the higher frequencies; the slope of the
suppression is less than desirable. At the frequencies in question,
however, the method is unsurpassed in simplicity and ease of use.
AUDIO EQUALIZER
A useful application which takes advantage of the bias adjust pin is
an audio equalizer circuit in Figure 7. An audio equalizer is a circuit
1991 Dec
6. For example, the drive capability of the amplifier is severely
M
All in one: NE5230
) of the input stage is reduced; this, in turn, lowers the -3dB
LAMP
#385
EE
C
1 F
pin, the output becomes severely attenuated. The
2
R
2
510
R
100
1
+
–
5230
10k*
+
–
C
100
1 F
1
*CALRAD 25-410
f
510
OSC
2
Figure 5. Gated Function Generator
1
RC
CC
EE
pin can
pin,
V
CC
4
100k
50k
which divides the audio frequency spectrum into equal parts.
Adjustments of the frequency response of each band are possible.
The equalizer circuit replaces a tone control in conventional audio
equipment. Used in conjunction with a series capacitor filter, the
NE5230 can be configured as a band pass filter. With one amplifier
for each band, significant cost savings can be realized. The RC
network in front of the circuit is used to remove the out-of-band
response beyond the audio spectrum.
LOW FREQUENCY
These circuits are unity gain Sallen-Key filters. For the lower
frequency band, the NE5230 can be configured to attenuate all but
the lowest frequencies. Because the input parameters are
compromised to the point where system performance is severely
affected, the aforementioned unconventional method of upper band
suppression is not used for the lowest frequency range of the
equalizer. Instead, the upper end of this frequency band is
attenuated using a second-order unity gain low-pass filter. The lower
end is DC. The upper end cutoff was chosen to be about 1000Hz.
50k
T
O
- V
EE
50k
–
+
2N2222
5230
C
2
1
1.0
+
–
-3dB BNDWIDTH (kHz) (LOG SCALE)
Figure 6. R
10k
10k
ADJ
10
vs Bandwidth
–
+
5230
50k
+
–
100
AN1512
Application note
SL00908
SL00909