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參數資料
| 型號： | PGA2500 |
| 英文描述： | Digitally Controlled Microphone Preamplifier |
| 中文描述： | 數控麥克風前置放大器 |
| 文件頁數： | 8/16頁 |
| 文件大?。?/td> | 197K |
| 代理商： | PGA2500 |
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SBOS289A NOVEMBER 2003 REVISED DECEMBER 2003
www.ti.com
8
Two external capacitors are required for the DC servo
function, with one capacitor connected between C
S11
and
C
S12
(pins 24 and 23), and the second capacitor connected
between C
S21
and C
S22
(pins 22 and 21). Capacitor values
up to 4.7
μ
F may be utilized. However, larger valued
capacitors will result in longer settling times for the DC
servo loop. A value of 1
μ
F is recommended for use in most
microphone preamplifier applications.
The PGA2500 includes a common-mode servo function.
This function is enabled and disabled using the CM bit in
the serial control word; see Figure 2. When enabled, the
servo provides common-mode negative feedback at the
input differential pair, resulting in very low common-mode
input impedance. The differential input impedance is not
affected by this feedback. This function is useful when the
source is floating, or has a high common-mode output
impedance. In this case, the only connection between the
source and the ground will be through the PGA2500
preamplifier input resistance.
In this case, input common-mode parasitic current is
determined by high output impedance of the source, not by
input impedance of the amplifier. Therefore, input
common-mode interference can be reduced by lowering
the common-mode input impedance while at the same
time not increasing the input common-mode current.
Increasing common-mode current degrades common-
mode rejection. Using the common-mode servo, overall
common-mode rejection can be improved by suppressing
low and medium frequency common-mode interference.
The common-mode servo function is designed to operate
with a total common-mode input capacitance (including
the microphone cable capacitance) of up to 10nF. Beyond
this limit, stable servo operation is not ensured.
The common-mode voltage control input, named V
COM
IN
(pin 25), allows the PGA2500 output and input to be DC-
biased to a common-mode voltage between 0 and +2.5V.
This allows for a DC-coupled interface between the
PGA2500 preamplifier output and the inputs of common
single-supply audio ADCs.
A dedicated 0dB input (pin 8) is provided so that the gain
of the PGA2500 may be forced to unity without using the
serial port interface. The 0dB input overrides gain settings
made through the serial port. While the 0dB input is active
(forced high), the serial port register may be updated or
data may passed through the serial interface to other
PGA2500 devices in daisy-chain configuration. However,
any changes made in the gain will not take effect until the
0dB input is driven low.
The zero crossing control input, named ZCEN (pin 9), is
provided for enabling and disabling the internal zero
crossing detector function. Forcing the ZCEN input high
enables the function. Zero crossing detection is used to
force gain changes on zero crossings of the analog input
signal. This limits the glitch energy associated with
switching gain, thereby minimizing audible artifacts at the
preamplifier output. Since zero crossing detection can add
some delay when performing gain changes (up to 16ms
maximum for a detector timeout event), there may be
cases where the user may wish to disable the function.
Forcing the ZCEN input low disables zero crossing
detection, with gain changes occurring immediately when
programmed.
An overflow indicator output, OVR, is provided at pin 5.
The OVR pin is an active high, CMOS
-
logic
-
level output.
The overflow output is forced high when the preamplifier
output voltage exceeds one of two preset thresholds. The
threshold is programmed through the serial port interface
using the OL bit. If OL = 0, then the threshold is set to
5.1V
RMS
differential, which is approximately 1dB below
the specified output voltage range. If OL = 1, then the
threshold is set to 4.0V
RMS
differential, which is
approximately 3dB below the specified output voltage
range.
The PGA2500 includes four programmable digital outputs,
named GPO1 through GPO4 (pins 1 through 4,
respectively), which are controlled via the serial port
interface. All four pins are CMOS
-
logic-level outputs.
These pins may be used to control relay drivers or
switches used for external preamplifier functions,
including input pads, filtering, polarity reversal, or phantom
power.
ANALOG INPUTS AND OUTPUTS
An analog signal is input differentially across the V
IN
+ (pin
27) and V
IN
(pin 26) inputs. The input voltage range and
input impedance are provided in the Electrical
Characteristics table. The Applications Information
section of this datasheet provides additional details
regarding typical input circuit considerations when
interfacing the PGA2500 to a microphone input.
Both V
IN
+ and V
IN
are biased at approximately 0.65V
below the common-mode input voltage, supplied at
V
COM
IN (pin 25). The use of AC
-
coupling capacitors (see
Figure 7, page 12) is highly recommended for the analog
inputs of the PGA2500. If DC
-
coupling is required for a
given application, the user must take this offset into
account.
It is recommended that a small capacitor be connected
from each analog input pin to analog ground. Values of at
least 50pF are recommended. See Figure 7 (page 12) for
larger capacitors being used for EMI filtering which will
satisfy this requirement.
The analog output is presented differentially across V
OUT
+
(pin 17) and V
OUT
(pin 16). The output voltage range is
provided in the Electrical Characteristics table. The analog
output is designed to drive a 600
differential load while
meeting the published THD+N specifications and typical
performance curves.
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相關代理商/技術參數 |
參數描述 |
|---|---|
| PGA2500_06 | 制造商:BB 制造商全稱:BB 功能描述:Digitally Controlled Microphone Preamplifier |
| PGA2500EVM | 功能描述:音頻 IC 開發(fā)工具 PGA2500 Eval Mod RoHS:否 制造商:Texas Instruments 產品:Evaluation Kits 類型:Audio Amplifiers 工具用于評估:TAS5614L 工作電源電壓:12 V to 38 V |
| PGA2500IDB | 功能描述:傳聲器前置放大器 GainRange:0dBand RoHS:否 制造商:Texas Instruments 可用增益調整:Digital control, 65 dB to 0 dB 共模抑制比（最小值）: 輸入補償電壓: 最大輸入電阻:9200 Ohms 最大工作溫度:+ 85 C 封裝 / 箱體:SSOP-28 封裝:Tube |
| PGA2500IDBG4 | 功能描述:傳聲器前置放大器 0dB & 10dB-65dB in 1dB steps RoHS:否 制造商:Texas Instruments 可用增益調整:Digital control, 65 dB to 0 dB 共模抑制比（最小值）: 輸入補償電壓: 最大輸入電阻:9200 Ohms 最大工作溫度:+ 85 C 封裝 / 箱體:SSOP-28 封裝:Tube |
| PGA2500IDBR | 功能描述:傳聲器前置放大器 0dB & 10dB-65dB in 1dB steps RoHS:否 制造商:Texas Instruments 可用增益調整:Digital control, 65 dB to 0 dB 共模抑制比（最小值）: 輸入補償電壓: 最大輸入電阻:9200 Ohms 最大工作溫度:+ 85 C 封裝 / 箱體:SSOP-28 封裝:Tube |
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