6270 GAIN CONTROLLED MICROPHONE PREAMPLIFIER VOGAD

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					                6270 GAIN CONTROLLED MICROPHONE
                       PREAMPLIFIER / VOGAD
The 6270 is a silicon integrated circuit combining the
functions of audio amplifier and voice operated gain adjusting
device (VOGAD).

It designed to accept signals from a low sensitivity microphone
and to provide an essentially constant output signal for a 50dB range of
input. The dynamic range, attack and decay times are controlled by                                                               DIP-8
external components.                                                                                                      (Plastic Package)


FEATURES
•     Constant Output Signal
•     Fast Attack
•     Low Power Consumption
•     Simple Circuitry                                                                                                             SO-8
                                                                                                                          (Plastic Micropackage)
APPLICATIONS
                                                                                                                      ORDERING NUMBER:
•     Audio AGC Systems                                                                                             6270CDP        Plastic
•     Transmitter Overmodulation Protection                                                                         6270MP8        Plastic Micropackage
•     Tape Recorders

QUICK REFERENCE DATA
•     Supply Voltage : 4.5V to 10V
•     Voltage Gain : 52dB

    ABSOLUTE MAXIMUM RATINGS
                                                                                            AGC TIME CONST            1             8    MAIN AMP OUTPUT
    Supply Voltage: 12V
    Storage temperature : -55ºC to +125ºC                                                   PREAMP OUTPUT             2             7    MAIN AMP INPUT

                                                                                                             Vcc      3             6    0V

                                                                                             PREAMP INPUT             4             5    PREAMP INPUT



                                                                                                      Pin connections 6270 (top view)
    BLOCK DIAGRAM
                                                     Vcc

                                           100n
                                                                  PRE AMP             MAIN AMP
                                                                  OUTPUT              INPUT
                                                          3                 2     7

                                                                                            10k


                                                                            680
                                               4 180
                                                                                                                    MAIN AMP
                                     PRE AMP                                                                       8 OUTPUT
                                      INPUT    5

                                                   180
                                                                   AGC                 2k
                                                                                                     AGC
                                                                                                  DETECTOR




                                                   EARTH      6                 1     AGC TIME
                                                                                      CONSTANT
                                                                      CT              RT
  GAIN CONTROLLED MICROPHONE PREAMPLIFIER/VOGAD                                                                                6270



ELECTRICAL CHARACTERISTICS
Test conditions (unless otherwise stated) :
Supply voltage Vcc : 6V
Input signal frequency : 1kHz
Ambient temperature : -30ºC to +85ºC
Test circuit shown in Fig. 1


                                                                 Value
               Characteristic                                                          Units                     Conditions
                                                Min             Typ          Max
Supply current                                                  5            10        mA
Input impedance                                                 150                    Ω                  Pin 4 or 5
Differential input impedance                                    300                    Ω
Voltage gain                                   40               52                     dB                 72V rms input pin 4
Output level                                   55               90           140       mV rms             4mV rms input pin 4
THD                                                             2            5         %                  90mV rms input pin 4
Equivalent noise input voltage                                  1                      V                 300Ω source, 400Hz to 25kHz bandwidth




               +6V                                                                                                     EXTERNAL
                                                                                                                          4.7n
                                2.2


                                                     4.7n                                                                10k

                                                                                                   EXTERNAL
                          1             8                       OUTPUT                      680       2.2
                                                      10   (1k MIN LOAD)                                                            8
                          2             7

                          3             6

                          4             5                                                          2         7

         47
1M                      INPUT          INPUT

                 100n                          22k                                            10k
                                                                             Voltage gain =
                                                                                              680
N.B. If input not AC coupled the resistance                                  Upper frequency response 10kΩ/4.7nF = 3kHz
    between pins 4 and 5 must be less than 10 ohms                           Lower frequency response 680Ω/2.2F = 300Hz


        Fig.1 6270 test and application circuit                                    Fig.2 6270 frequency response

APPLICATION NOTES
Voltage gain
     The input to the 6270 may be single ended or differential                    The 6270 has an open loop upper frequency response of a
but must be capacitor coupled. In the single-ended mode the signal           few MHz and a capacitor should be connected between pins 7 and 8
can be applied to either input, the remaining input being decoupled to       to give the required bandwidth.
ground. Input signals of less than a few hundred microvolts rms are               Attack and delay times
amplified normally but as the input level is increased the AGC begins             Normally the 6270 is required to respond quickly by holding
to take effect and the output is held almost constant at 90mV rms over       the output level almost constant as input is increased. This attack
an input range of 50dB.                                                      time, the time taken for the output to return to within 10% of the origi-
     The dynamic range and sensitivity can be reduced by reducing            nal level following a 20dB increase in input level, will be approxima-
the main amplifier voltage gain. The connection of a 1k resistor betwe-      tely 20ms with the circuit of Fig.1. It is determined by the value of the
en pins 7 and 8 will reduce both by approximately 20dB. Values less          capacitor connected between pin 1 and ground and can be calculated
than 680Ω are not advised.                                                   approximately from the formula :
     Frequency response                                                           Attack time = 0.4ms/F
     The low frequency response of the 6270 is determined by                      The decay time is determined by the discharge rate of the capaci-
the input, output and coupling capacitors. Normally the coupling capa-       tor and the recommended circuit gives a decay rate of 20dB/second.
citor between pins 2 and 7 is chosen to give a – 3dB point at 300Hz,         Other values of resistance between pin 1 and ground can be used to
corresponding to 2.2F, and the other capacitors are chosen to give          obtain different results.
a response to 100Hz or less.
          GAIN CONTROLLED MICROPHONE PREAMPLIFIER/VOGAD                                                                                                                                                     6270




                                          100

                                           90
                                                                                                                        60




                                                                                                    VOLTAGE GAIN (dB)
                OUTPUT, PI N 8 (mV RMS)




                                           80
                                                                                                                        50
                                           70
                                                                                                                        40
                                           60
                                                              Vs = +6V, T A = +25o C, f = 1kHz                          30
                                           50
                                                                                                                        20
                                           40

                                           30                                                                           10

                                           20                                                                           0
                                                10V      100V       1mV        10mV       100mV                                  1kHz                                      10kHz        100kHz         1MHz      10MHz
                                                                  INPUT (RMS)                                                                                                         FREQUENCY
                                          Fig. 3 Voltage gain (single ended input) (typical)                                                                       Fig. 4 Open loop frequency response (typical)




                                           0                                                                                                                       0
(dB RELATIVE TO WANTED OUTPUT)
  OUTPUT DISTORTION PRODUCTS




                                                                                                                            O UTPUT INT ERMO DULATIO N PRO DUCTS
                                          -10                                                                                    (dB RELA TIV E TO EA CH TO NE)    -10

                                          -20                                                                                                                      -20
                                                                        Vs = 6V, f = 1kHz
                                          -30                                                                                                                      -30
                                                                                                                                                                                               Vs = 6V

                                                                                                                                                                   -40
                                          -40
                                                                                                                                                                                     THIRD ORDER
                                                                                                                                                                   -50
                                          -50       SECOND HARMONIC
                                                                                                                                                                                      FIFTH ORDER
                                                          THIRD HARMONIC                                                                                           -60
                                          -60
                                                                                                                                                                   -70

                                                1                      10                   100                                                                          1                    10                   100
                                                          SINGLE ENDED INPUT (mV RMS)                                                                                                SINGLE ENDED INPUT (mV RMS)


                                                     Fig. 5 Overload characteristics (typical)                 Fig. 6 Typical Intermodulation distortion (1.55 and 1.85kHz tones)
GAIN CONTROLLED MICROPHONE PREAMPLIFIER/VOGAD                  6270




        05                                                04




        06                                                03
                                     5   4



                              6                  3


                              7

                                             2



                              8                  1



        07                                                02




                      08                             01



                              Bonding diagram of 6270
GAIN CONTROLLED MICROPHONE PREAMPLIFIER/VOGAD                                                       6270




       1.17mm        8                    7                  6




                                                                                 5



   Y                                                                             4

                         1                    2             3



                                                  1.45mm


                               X

                                        Pads location of 6270

                                                                      2
  Die size Хr=1.45mm, Уr=1.17mm (pad size 116 х 116 mkm )
  Coordinates of pads
       No of pad                   Xmin                Xmax                Ymin          Ymax
                              (left bottom)         (right top)       (left bottom)   (right top)
                1                    97                 213                  94           210
                2                   534                 650                  94           210
                3                   771                 887                 112           228
                4                  1240                1356                 214           330
                5                  1240                1356                 400           516
                6                   706                 812                 929          1045
                7                   442                 558                 929          1045
                8                   106                 222                 929          1045

  DESCRIPTION
        Pin                  No of pad                            Function
                01                 01         AGC Time Constant
                02                 02         PRE AMP Output
                03                 03         Vcc
                04                 04         PRE AMP Input
                05                 05         PRE AMP Input
                06                 06         EARTH (0 V)
                07                 07         MAIN AMP Input
                08                 08         MAIN AMP Output

				
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Description: 6270 GAIN CONTROLLED MICROPHONE PREAMPLIFIER VOGAD