SSM2163_15 Datasheet, PDF (12/16 Pages) Analog Devices – Digitally Controlled 8 3 2 Audio Mixer

SSM2163
MIXER
ATTENUATOR
BUFFER AMP MIXER SUMMING
AMPLIFIER
V_IN
MIXER
SWITCH
Σ
V_OUT
CHANNEL
SELECT
AGND
V_OUT
+5V
+5V
POWER
SUPPLY
+
10µF
V_CC V_{DD AGND}
0.1µF
SSM2163 _ACOM
V_SS V_{EE DGND}
0.1µF
+
10µF
V_CC
R1
ACOM
R2
R1=R2
V_EE
10µF 0.1µF
V_EE
GND
TTL/CMOS
LOGIC
CIRCUITS
Figure 24. Use Separate Traces to Reduce Power Supply
Figure 23. Single-Supply Pseudo-Ground Reference
Noise
OBSOLETE (ACOM) Generator
For single supply operation, the inputs can either be ac-coupled,
as shown in Figure 25, or referenced to the pseudo-ground out-
put. AC coupling eliminates dc offset and offset drift
differentials between the input source and the SSM2163. In
addition, ac coupling reduces the risk of “clicks” when switching
between multiple dc-coupled inputs which have different
reference levels.
Since the input coupling capacitors are in series with the 10 kΩ
input of the attenuator, the impedance of these capacitors will
influence low frequency gain. The inexpensive 10 µF aluminum
electrolytic capacitors shown will limit the gain error to 0.66 dB
at 20 Hz.
If the entire system is operating from a single supply, then
typically the input voltage is already referenced to the midpoint
of the supply. In this case, the SSM2163 can be referenced to
the same midpoint reference source, as shown in Figure 22c.
Even if the system includes separate analog and digital power
supplies, both the analog and digital power pins of the
SSM2163 should be connected to the analog supply. While this
connection will inject a small amount of digital noise into the
analog ground, the effect is small due to the SSM2163’s low
digital logic input currents and capacitances. If, on the other
hand, the SSM2163’s digital supply pins are connected to a
digital power supply, then noise from the digital supply will be
coupled into the SSM2163 and degrade performance.
APPLICATIONS
An 8-Input, 2-Output Mixer
A single-chip, 8-input, 2-output mixer using the SSM2163 is
shown in Figure 25. With this circuit, any of the eight channels
can be attenuated by 0 dB to –63 dB and mixed into the right,
left, or both outputs under software control.
+5V
This connection will eliminate dc offset errors caused by having
4
10
+
10µF
0.1µF
the input signal common and the SSM2163 analog common
referenced to different voltages. DC offset errors can also be
INPUT 1 LEFT
10µF 5
+
V_IN1
V_DD V_CC
eliminated, of course, by using the ac coupling technique
discussed above.
Dual-Supply Operation
INPUT 2 LEFT
INPUT 3 LEFT
INPUT 4 LEFT
10µF ₂₂
+
10µF 7
+
10µF 20
+
V_IN2
V_IN3
V_IN4
V_OUTL ¹⁴
V_OUTR ¹⁵
LEFT CHANNEL
OUTPUT
RIGHT CHANNEL
OUTPUT
The SSM2163 will also operate from dual supplies, ranging
from ± 4 V to ± 7 V. (See Figure 22a.) In this case, input signals
can be referenced to power supply ground. The ACOM output
(Pin 13) is left open (no connection) for dual supply operation.
Supply Decoupling
Optimizing the performance of the SSM2163, or any low noise
device, requires careful attention to power supply decoupling.
Since the SSM2163 can operate from a single +5 V supply, it
INPUT 1 RIGHT
INPUT 2 RIGHT
INPUT 3 RIGHT
INPUT 4 RIGHT
DATA IN
CLOCK
10µF
+
9
V_IN5
DATA OUT ³ NC
10µF
+
18
V_IN6
10µF
+
11
V_IN7
SSM2163
SHIELD
6
10µF _{16 VIN8}
+
SHIELD ⁸
SHIELD ¹⁹
27
DATA IN
21
SHIELD
26 _CLK
SHIELD ²³
seems convenient to simply tap into the digital logic power
CHIP SELECT
25
WRITE
AGND ¹⁷
supply. Unfortunately, the logic supply is often a switch-mode
design, which generates noise in the 20 kHz to 1 MHz range. In
addition, fast logic gates can generate glitches hundred of millivolts
in amplitude due to wiring resistances and inductances.
SYSTEM MUTE
24
LD
28 _SYSMUTE
V_SS
2
13
ACOM
V_EE DGND
12
1
+
10µF
0.1µF
If a separate analog power supply is not available, the SSM2163
can be powered directly from the system power supply. Separate
power and ground traces should be provided for the analog
section, if possible. This arrangement, shown in Figure 24, will
isolate the analog section from the logic switching transients.
Even if a separate power supply trace is not available, however,
generous supply bypassing will reduce supply line induced
noise. Local supply bypassing, consisting of a 10 µF tantalum
electrolytic in parallel with a 0.1 µF ceramic capacitor, is
recommended in all applications. (See the SSM2163 Power
Supply Connections figures.)
Figure 25. An 8-Input, 2-Output Mixer
This circuit demonstrates ac coupling of the inputs. As
previously mentioned, this eliminates level shifting concerns
from previous stages.
The circuit of Figure 25 also demonstrates single +5 V supply
operation. The output of the ACOM supply-splitter, Pin 13,
provides the pseudo-ground reference which is required when
operating from a single supply.
–12–
REV. 0