LC502 Просмотр технического описания (PDF) - Gennum -> Semtech
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LC502 Datasheet PDF : 5 Pages
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While the automatic gain control is operating the output
signal varies by less than 6dB for an input signal variation
of 40dB. The attack time of the gain control (circuit in
Figure 1) is approximately 2ms and the release time
approximately 1s. The release time can be increased or
decreased by selecting a larger or smaller value for capacitor
C2. The second block, employing the LC507, is a three
stage inverting amplifier with an open loop gain of approximately
70dB. The DC operating point, as well as the overall gain,
can be set by selecting the feedback resistors RF, RD, R2
and R3 accordingly. The DC operating point is very stable
because the input of the LC507 is AC coupled and the DC
gain is low. This is particularly important when the amplifier
is powered from a 1.2 or 1.5V cell.
The gain of this second section (LC507) can be adjusted
by changing the values of R2 and R3. It is recommended
to increase R2 for lower gains and R3 for higher gains. The
magnitude of the maximum output levels are power supply
dependent (Table 1).
The recording head is coupled to the amplifier through R4
and C9. The value of these components depend on the
head characteristics. R4 sets the recording current at low
frequencies, according to the head specification and the
type of magnetic tape used. C9 compensates for the
increase in head impedance at high frequencies. The
component values for different power supply (battery)
voltages are shown in Table 2.
Table 1
Maximum Output Levels Units
Power Supply (battery) V 1.1 to 1.6 2 to 3.5 4 to 6.5
V
Output Level VRMS
0.15
0.35
1
VRMS
Table 2
Parameter
Component Values
LC507 & LD502
Units
Power Supply (battery) V 1.1 to 1.6 2 to 3.5 4 to 6.5 V
RF
0
0
100
kΩ
RD
N/A
N/A
47
kΩ
RC
0.68
1
1.8
kΩ
R3
100
200
100
kΩ
10
5
0
-5
-10
-15
-20
-25
0.1
1
FREQUENCY (kHz)
10
20
Fig. 2 Recording Amplifier
without Equalization
20
10
5
0
-5
-10
-15
-20
-25
-30
-35
-40
-120
-100
-80
-60
-40
-20
0
INPUT (dBV)
Fig. 3 AGC Characteristic of the
Recording Amplifier
The frequency response of the recording amplifier (out-
put at point B, 2.2kΩ source resistance and 50 µV at
point A) is shown in Figure 2.
The AGC characteristic is shown in Figure 3. Different
microphone connections are shown in Figure 4 and
Figure 5.
500 - 64 - 4
2
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