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參數(shù)資料
| 型號(hào)： | SSM2018TPZ |
| 廠商： | Analog Devices Inc |
| 文件頁(yè)數(shù)： | 3/16頁(yè) |
| 文件大?。?/td> | 0K |
| 描述： | IC AMP AUDIO MONO CLASS AB 16DIP |
| 標(biāo)準(zhǔn)包裝： | 25 |
| 放大器類型： | 音頻 |
| 電路數(shù)： | 1 |
| 轉(zhuǎn)換速率： | 5 V/µs |
| 增益帶寬積： | 14MHz |
| 電流 - 輸入偏壓： | 250nA |
| 電壓 - 輸入偏移： | 1000µV |
| 電流 - 電源： | 11mA |
| 電壓 - 電源，單路/雙路(±)： | 10 V ~ 36 V，±5 V ~ 18 V |
| 工作溫度： | -40°C ~ 85°C |
| 安裝類型： | 通孔 |
| 封裝/外殼： | 16-DIP（0.300"，7.62mm） |
| 供應(yīng)商設(shè)備封裝： | 16-PDIP |
| 包裝： | 管件 |
| 產(chǎn)品目錄頁(yè)面： | 775 (CN2011-ZH PDF) |
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REV. B
–11–
SSM2018T
As explained above, the gain constant has a –3500 ppm/
∞C that
is due to its reciprocal dependence on absolute temperature.
This will cause the gain to vary by 7 dB over the temperature
range from –40
∞C to +85∞C when the nominal gain at room
temperature is set to 20 dB. Of course, the gain change is quite
small if the temperature range of operation is restricted. Never-
theless, the TC of the gain constant is easily compensated by
buffering the control voltage to the VCA with a circuit having a
3500 ppm/
∞C temperature coefficient. Figure 4 shows a simple
solution to the problem using an op amp with a PT146 tem-
perature compensating resistor from the Precision Resistor
Company. Note that this circuit is inverting, which will change
the gain constant to a positive quantity. Any other circuit that
provides the necessary positive TC will work.
Digital Control of the Gain
A common method of controlling the gain of a VCA is to use a
digital-to-analog converter to set the control voltage. Figure 5
shows a 12-bit DAC, the DAC8512, controlling the SSM2018T.
The DAC8512 is a complete 12-bit converter in an 8-pin pack-
age. It includes an on-board reference and an output amplifier
to produce an output voltage from 0 V to 4.095 V, which is 1
mV/bit. Since the voltage is always positive, this circuit only
provides attenuation. The resistor divider on the output of the
DAC8512 is set to scale the output voltage so that full scale
produces 80 dB of attenuation. The resistor divider can be
adjusted to provide other attenuation ranges. If a parallel inter-
face is needed, then the DAC8562 may be used or, for a dual
DAC, the AD8582.
0.1 F
+15V
18k
VIN
DAC8512
CS
CLR
0.1 F
18k
50pF
47pF
VOUT
150k
+15V
–15V
0.1 F
+5V
CCON
1 F
R6
825
R7
1k
0V
VC
+2.24V
LD
SCLK
SDI
SSM2018T
NC
NC = NO CONNECT
Figure 5. 12-Bit DAC Controls the VCA Gain
Supply Considerations and Single Supply Operation
The SSM2018T has a wide operating supply range. Many of the
graphs in this data sheet show the performance of the part from
±5 V to ±18 V. These graphs offer typical performance specifi-
cations and are a good indication of the parts’ capabilities. The
minimum operating supply voltage is
±4.5 V. Below this voltage,
the parts are inoperable. Thus, to account for supply variations,
the recommended minimum supply is
±5 V.
For simplicity the circuits in the data sheet do not show supply
decoupling; however, to ensure best performance, each supply pin
should be decoupled with a 0.1
mF ceramic (or other low resistance
and inductance type) capacitor as close to the package as possible.
This minimizes the chance of supply noise feeding through the part
causing excessive noise in the audio frequency range.
The SSM2018T can be operated in single supply mode as long
as the circuit is properly biased. Figure 6 shows the proper con-
figuration, which includes an amplifier to create a false ground
node midway between the supplies. A high quality, wide band-
width audio amplifier, such as the OP176 or AD797, should
be used to ensure a very low impedance ground over the full
audio frequency range. The minimum operating supply for the
SSM2018T is
±5 V, which gives a minimum single supply of
+10 V and ground. The performance of the circuit with +10 V
is identical to graphs that show operation of the SSM2018T
with
±5 V supplies.
Operational Voltage Controlled Element
The SSM2018T has considerable flexibility beyond the basic VCA
circuit utilized throughout this data sheet. The name “Operational
Voltage Controlled Element” comes from the fact that the part
behaves much like an operational amplifier with a second voltage
controlled output. The symbol for the OVCE connected as a unity
gain follower/VCA is shown in Figure 7. The voltage output labeled
V1–G is fed back to the inverting input just as it is for an op amp’s
feedback. The VG output is amplified or attenuated depending
upon the control voltage.
V+
1 F
RB
18k
V+
18k
VIN+
1 F 18k
VIN–
47pF
1 F
50pF
1k
VCONTROL
3k
VOUT
SSM2018T
V+
OP176
100k
V+
10 F
Figure 6. Single Supply Operation of SSM2018T
Because the OVCE works just like an op amp, the feedback could
as easily have included resistors to add gain, or a filter network
to add frequency shaping. The full circuit for the OVCE is shown
in Figure 8. Notice that the amplifier whose output (Pin 16) was
originally connected to VMINUS is now the output for feedback.
As mentioned before, because the SSM2018T is trimmed for
the basic VCA configuration, potentiometers are needed for the
OVCE configuration to ensure the best THD and control
feedthrough performance.
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