OP470_15 Datasheet, PDF (13/16 Pages) Analog Devices – Very Low Noise Quad Operational Amplifier

OP470
100
100
90
A OUT 90
10
A OUT 10
0%
0%
5V
5V
1ms
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%.
Figure 16. Digital Panning Control Output
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.
5V
SIDE A IN
DAC-8408GP V_DD
R_FBA
V_REFA
DAC A
I_OUT1A
20pF
+15V
1/4
OP470E
A OUT
I_OUT2A/2B
DAC B
I_OUT1B
R_FBB
SIDE B IN
V_REFC
DAC C
R_FBC
I_OUT1C
DAC DATA BUS
PINS 9 (LSB) – 16 (MSB)
1k⍀
5V
A/B
1k⍀
R/W
DS1
DAC SELECT
DS2
I_OUT2C/2D
DAC D
I_OUT1D
DGND
R_FBD
–15V
1/4
20pF ^OP470E
20pF
1/4
OP470E
1/4
20pF ^OP470E
A OUT
B OUT
B OUT
Figure 15. Digital Panning Control Circuit
REV. B
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