CXA1917AS SONY [Sony Corporation], CXA1917AS Datasheet - Page 12

• Manufacturer Part Number: CXA1917AS
• Description: Dolby S type Noise Reduction Processor
• Manufacturer: SONY [Sony Corporation]

Notes on Application
The CXA1917A is an encoding IC for the Dolby S type (NR). An external operational amplifier is required to
configure the decoder circuit. The Dolby level voltage of this IC is designed to be –6dBm (388mVrms), which is
the same as that of the CXA1562 and CXA1563 Dolby B-C type ICs. Therefore, it is possible to use the
CXA1562 or the CXA1563 to configure a B-C-S type switchable processor. The B-C-S type switchable
processor can be configured without requiring an external operational amplifier because the CXA1563 has a
built-in S-type changeover switch.
Power Supply
The CXA1917A will operate with either dual or single power supply. Connect VCT pin to GND pin when dual
power supply is used. Connect V
power supply half the Vcc generated inside the IC is generated at VCT pin.
The supply voltage range is from ±4.5V to ±6.5V and from 9V to 13V for dual and single power supplies,
respectively. Note, however, that the minimum supply voltage is determined by the maximum voltage
amplitude of external operational amplifier. Because general-purpose operational amplifiers have the
maximum voltage amplitude of approximately (Vcc – V
the 15dB overload margin, are ±5.0V and 10V for dual and single power supplies, respectively. The supply
current does not depend so much on the supply voltage, but does depend on the signal level and frequency.
The maximum supply current in the worst case is approximately 25mA.
Recording Processor
Fig. 1 shows the recording processor. The gain is defined as follows:
The processor in Fig. 1 has a gain of 14dB, therefore, input sensitivity is –20dBm (77.5mVrms). An input
sensitivity higher than –25dBm (44mVrms) is generally unacceptable due to noise performance, although this
is affected by the operational amplifier in the input circuit. An important characteristic for the external
operational amplifier is the noise performance for approximately an input impedance of 20kΩ. A bipolar input
type will be better than the JFET input type for the recording processor.
Playback Processor
Fig. 2 shows the playback processor. The gain is defined as follows:
The processor in Fig. 2 has a gain of 20dB, therefore, the input sensitivity is –26dBm (39mVrms). Important
characteristics of the playback processor are the frequency response and the feedback loop stability, which
depend on the gain of the feedback loop gain and the slew rate of the external operational amplifier. The slew
rate has to be higher than 3V/µs. The loop gain can be estimated using the gain bandwidth product BG (Hz) of
the operational amplifier and the decode gain APB. The lower limit of BG/APB is approximately 500kHz, and
the recommended range is from 1 to 3MHz.
Switchable Processor
Fig. 3 shows the switchable processor. The gains are the same as in equations (1) and (2). An operational
amplifier is required with low noise, average slew rate (> 3V/µs), and wide bandwidth (≈ 10MHz) for this gain
setting. A bipolar input type operational amplifier with a wide bandwidth like those of the 4560 and the 4570 is
required of the switchable processor.
The processor in Fig. 3 may generate a significant switching noise, especially when S2 switch is make-break-
make type. When S2 switch is a make-to-make type or has a quick switching feature, the switching noise will
be within the range acceptable for cassette decks with output muting circuits.
GREC20 · Log (1 + R62/R63) ...... (1)
GPB20 · Log (1 + R64/R65) ...... (2)
EE
pin to GND pin and open VCT pin when a single power supply is used. The
– 12 –
EE
) –2V, actual minimum supply voltages, which satisfy
CXA1917AM/AS