OP470ARCMDA AD [Analog Devices], OP470ARCMDA Datasheet - Page 13

• Manufacturer Part Number: OP470ARCMDA
• Description: Very Low Noise Quad Operational Amplifier
• Manufacturer: AD [Analog Devices]

Figure 14. Noise Density of Low Noise Amplifier, G = 1000
DIGITAL PANNING CONTROL
Figure 15 uses a DAC-8408, quad 8-bit DAC to pan a signal
between two channels. The complementary DAC current out-
puts two of the DAC-8408’s four DACs drive current-to-voltage
converters built from a single quad OP470. The amplifiers have
complementary outputs with the amplitudes dependent upon
the digital code applied to the DAC. Figure 16 shows the comple-
mentary outputs for a 1 kHz input signal and digital ramp applied
to the DAC data inputs. Distortion of the digital panning con-
trol is less than 0.01%.
REV. B
100
0%
90
10
SIDE A IN
SIDE B IN
PINS 9 (LSB) – 16 (MSB)
5V
DAC SELECT
DAC DATA BUS
1k
1k
Figure 15. Digital Panning Control Circuit
DAC-8408GP
V
V
A/B
R/W
DS1
DS2
REF
REF
A
C
DGND
DAC A
DAC B
DAC C
DAC D
V
5V
DD
–13–
I
I
OUT2A/2B
OUT2C/2D
I
OUT1A
I
I
I
R
R
R
R
OUT1B
OUT1C
OUT1D
Gain error due to the mismatching between the internal DAC
ladder resistors and the current-to-voltage feedback resistors is
eliminated by using feedback resistors internal to the DAC. Of
the four DACs available in the DAC-8408, only two DACs, A
and C, actually pass a signal. DACs B and D are used to pro-
vide the additional feedback resistors needed in the circuit. If
the VREFB and VREFD inputs remain unconnected, the
current-to-voltage converters using RFBB and RFBD are unaf-
fected by digital data reaching DACs B and D.
FB
FB
FB
FB
A
B
C
D
A OUT
A OUT
Figure 16. Digital Panning Control Output
20pF
20pF
20pF
20pF
100
0%
90
10
1/4
OP470E
1/4
OP470E
1/4
OP470E
1/4
OP470E
5V
+15V
–15V
5V
A OUT
A OUT
B OUT
B OUT
1ms
OP470