CXA1797 SONY [Sony Corporation], CXA1797 Datasheet - Page 24

• Manufacturer Part Number: CXA1797
• Description: Dolby B-C Type Noise Reduction System with Recording Equalizer Amplifier
• Manufacturer: SONY [Sony Corporation]

5. NR TC, BC TC, STC, RMUTE TC
6. Meter circuit
7. Bias circuit
These time constants are set in order to prevent the generation of a popping noise when one of the
switches operates. In addition, these functions can be controlled directly by applying voltage from an
external source. (In this case, the capability to drive 17 kΩ impedance is required.)
The CXA1797Q meter circuit is a logarithmic detector.
The circuit has a sensitivity of 65 mV/dB and is designed to generate 2.8 V when the reference signal is
input.
This circuit has the temperature characteristics depend on Vt (= KT/q).
As a result, in order to satisfy the specifications, sufficient warmup time is required.
If METER GAIN is set to HIGH mode, the sensitivity is increased by 12 dB.
The METER AC pin is used to detect only the AC component, the low-frequency cut-off is determined by
the 8.5 kΩ internal resistance and the capacitance connected to this pin.
(With approximately 20 kHz at 1 µF, the high-frequency cut-off is fixed at 20 kHz.)
This circuit generates the DC voltage that controls the bias oscillator.
The BIASOUT voltage is specified so that voltage equal to the internal reference voltage (V
generated at a pin selected according to the tape mode (BIAS N, BIAS C, or BIAS M).
The BIASOUT pin is provided with a protective resistor of 147 Ω. Take into account the corresponding
voltage drop when the load current is high.
V
EE
METAL
—24—
17k
CrO
NORM
147
2
V
EE
EE
+ 1.25 V) is
CXA1797Q