LC502 Ver la hoja de datos (PDF) - Gennum -> Semtech
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LC502 Datasheet PDF : 5 Pages
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3. Low Parts Count “Economy” Recording Amplifier for Single Cell Operations
CIRCUIT DESCRIPTION
A minimum component count record amplifier for a 1.1 to
1.6V for single cell operations supply is shown in Figure 8.
The frequency response is the same as in Figure 2.
R1
130K
Gain
Set
+C1 IN
1.0
VR V+
LD502
OUT
+
C4
22
+C6
1
+
C5
22
R2
5.6K
GND
AGC
Filter
AGC
IN
+
C3
1.0
R3
100k
+
C2
22
1
4 LC507 2
3
+1.1 to 1.6V
RC
910
R4
C8
+
1.0
C9
+
C7 4.7nF
All resistors in ohms, all capacitors in farads unless otherwise stated
To Recording
Head
Fig. 8 Minimum Component Recording Amplifier
MIC
P
S1A
R
P
S1B
R
R/P
Head
DC
Bias
0.95V
+ C5
22
R6
470
VCC VR
R1
180k
C4 +
22 C15 R11
2.2nF 4.7k
C1
0.47
+
Gain
Set
LD502 OUT
IN
AGC AGC
GND Filter IN
C2
C3
2.2
1
+
+
R13
22k
R10
R7
47k
18k
C13
1.2nF
C14
1.5nF
C12
2.2nF
P
R
S1C
R2
5.6k
R12
5.6k
C6
+1
S1D
R4
27k
R8
R9
5.6k
10k
1
LC507
2
4
C11
2.2nF
3
R3
100K
R5
180k
C9
2.2nF
Headphones
P
R
S1E
All resistors in ohms, all capacitors in farads unless otherwise stated
Fig. 9 Recording/Playback Amplifier
GND
VCC
RC
C8 +
2.2
RF
C7
2.2nF
RD
With the switch S1 in the position shown in Figure 9, the
amplifier is in playback mode. In this mode the LD502 is
used as a linear feedback equalizer rather than an AGC
amplifier. To compensate for the head playback charac-
teristic in the low frequency range, the gain drops by 6dB
per octave as the frequency increases. The group R7,
R10 and C14 shapes the frequency response in the low
frequency range. R7, R8 and C12 boost the gain in the
high frequency range. The frequency response of the
playback amplifier has to match the head-tape charac-
teristics. Consequently the values of R7,R8, R10, C12
and C14 must be selected accordingly.
When powered from a single battery cell (1 to 1.6V) the
LC507 can drive a 600Ω earphone. For higher supply
voltages, a 1 kΩ earphone is more appropriate. With the
switch S1 in recording position the amplifier is configured as
in Figure 6. The frequency response of the playback ampli-
fier is shown in Figure 11 (Input 5mV at A, Output at B, Figure
10). The overall frequency response (record/playback) for
the circuit in Figure 9 measured for a tape speed of 1-7/8 ips
and a wavelength equivalent to approximately 10-12kHz is
shown in Figure 12.
500 - 64 - 4
4
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