AN6077 INTERSIL [Intersil Corporation], AN6077 Datasheet - Page 4

• Manufacturer Part Number: AN6077
• Description: An IC Operational Transconductance Amplifier With Power Capability
• Manufacturer: INTERSIL [Intersil Corporation]

DIFFERENTIAL
A = g
DIFFERENTIAL
FIGURE 10. SOME TYPICAL DIFFERENTIAL TO SINGLE
FIGURE 11. A DIFFERENTIAL TO SINGLE ENDED
DIFFERENTIAL
g
m
m
A = 10mS x 10K = 100.
R
INPUT
DIFFERENTIAL
L
INPUT
10mS.
INPUT
at 500 A, I
ENDED CONVERSION CIRCUITS
CONVERSION CIRCUIT WITHOUT PRECISION
RESISTORS
INPUT
2K
2K
ABC
3
2
:
+
-
-
+
+
-
-
+
R
R
1
3
4-4
+
-
5
CA3080
R
R
R
R
R
500 A
R
1
2
3
1
2
R
R
I
4
ABC
-
+
4
6
R
2
V-
R
R
7
4
R
1
2
R
R
7
+V
-
+
3
4
R
=
5
OUTPUT
R
R
OUTPUT
R
R
6
3
4
1
2
R
R
R
=
Application Note 6077
5
4
1
=
RL
10K
= R
R
R
OUTPUT
4
3
R
R
OUTPUT
3
6
7
The CA3094
The CA3094 offers a unique combination of characteristics
that suit it ideally for use as a programmable gain block for
audio power amplifiers. It is a transconductance amplifier in
which gain and open-loop bandwidth can be controlled
between wide limits. The device has a large reserve of
output-current capability, and breakdown and power dissipation
ratings sufficiently high to allow it to drive a complementary
pair of transistors. For example, a 12W power amplifier stage
(8 load) can be driven with peak currents of 35mA
(assuming a minimum output transistor beta of 50) and
supply voltages of 18V. In this application, the CA3094A is
operated substantially below its supply voltage rating of 44V
max. and its dissipation rating of 1.6W max. Also in this
application, a high value of open-loop gain suggests the
possibility of precise adjustment of frequency response
characteristics by adjustment of impedances in the feedback
networks.
Implicit Tone Controls
In addition to low distortion, the large amount of loop gain
and flexibility of feedback arrangements available when
using the CA3094 make it possible to incorporate the tone
controls into the feedback network that surrounds the entire
amplifier system. Consider the gain requirements of a
phonograph playback system that uses a typical high quality
magnetic cartridge[3]. A desirable system gain would result
in from 2W to 5W of output at a recorded velocity of 1cm/s.
Magnetic pickups have outputs typically ranging from 4mV to
10mV at 5cm/s. To get the desired output, the total system
needs about 72dB of voltage gain at the reference
frequency.
Figure 12 is a block diagram of a system that uses a passive or
“losser” type of tone control circuit that is inserted ahead of the
gain control. Figure 13 shows a system in which the tone
controls are implicit in the feedback circuits of the power
amplifier. Both systems assume the same noise input voltage
at the equalizer and main-amplifier inputs. The feedback
system shows a small improvement (3.8dB) in signal-to-noise
ratio at maximum gain but a dramatic improvement (20dB) at
the zero gain position. For purposes of comparison, the
assumption is made that the tone controls are set “flat” in both
cases.
Cost Advantages
In addition to the savings resulting from reduced parts count
and circuit size, the use of the CA3094 leads to further
savings in the power supply system. Typical values of power
supply rejection and common-mode rejection are 90dB and
100dB, respectively. An amplifier with 40dB of gain and 90dB
of power supply rejection would require 316mV of power
supply ripple to produce 1mV of hum at the output. Thus, no
further filtering is required other than that given by the energy
storage capacitor at the output of the rectifier system.