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The is a precision dual gain control circuit designed for low voltage applications. The NE/SA575's channel is an expandor, while channel 2 can be configured either for expandor, compressor, or automatic level controller (ALC) application.FEATURES
· Operating voltage range from to 7V· Reference voltage = 0dB· One dedicated summing op amp per channel and two extra
· 600 drive capability· Single or split supply operation· Wide input/output swing capability· 3000V ESD protectionAPPLICATIONS
· Portable communications· Cellular radio· Cordless telephone· Consumer audio
· Portable broadcast mixers· Wireless microphones· Modems· Electric organs· Hearing aids
DESCRIPTION 20-Pin Plastic Dual In-Line Package (DIP) 20-Pin Plastic Small Outline Large 20-Pin Plastic Shrink Small Outline Package (SSOP) 20-Pin Plastic Dual In-Line Package (DIP) 20-Pin Plastic Small Outline Large 20-Pin Plastic Shrink Small Outline Package (SSOP) TEMPERATURE RANGE to +85°C ORDER CODE SA575D SA575DK DWG SOT163-1 SOT266-1
RATING SYMBOL VCC VIN TA TSTG JA PARAMETER Single supply voltage Voltage applied to any other pin Operating ambient temperature range Storage temperature range Thermal impedance DIP SOL SSOP -65 to UNITS V °C °C/W
DC ELECTRICAL CHARACTERISTICS Typical values are = 25°C. Minimum and Maximum values are for the full operating temperature range: to 70°C for to +85°C for SA575, except SSOP package is tested at +25°C only. VCC = 5V, unless otherwise stated. Both channels are tested in the
Expandor mode (see Test Circuit) LIMITS SYMBOL PARAMETER TEST CONDITIONS MIN For compandor, including summing amplifier VCC ICC VREF RL THD ENO 0dB VOS Supply voltage1 Supply current Reference voltage2 Summing amp output load Total harmonic distortion Output voltage noise Unity gain level Output voltage offset Output DC shift 1kHz No signal No signal to 0dB Gain cell input 0dB, 1kHz Rectifier input 6dB, 1kHz Tracking error relative to 0dB Gain cell input 0dB, 1kHz Rectifier input 1kHz No signal VCC dB NE575 TYP MAX MIN SA575 TYP MAX UNITS
LIMITS SYMBOL PARAMETER Crosstalk For operational amplifier VO RL CMR CMRR IB VOS AVOL SR GBW ENI PSRR Output swing Output load Input common-mode range Common-mode rejection ratio Input bias current Input offset voltage Open-loop gain Slew rate Bandwidth Input voltage noise Power supply rejection ratio = 10k Unity gain Unity gain 1kHz, 250mV VIN 1kHz VCC-0.4 VCC VCC-0.4 VCC mV dB V/µs MHz µV dB TEST CONDITIONS MIN 1kHz, 0dB, CREF 220µF NE575 TYP -80 MAX -65 MIN SA575 TYP -80 MAX -65 dB UNITS
NOTES: 1. Operation down to VCC 2V is possible, but performance is reduced. See curves in Figure 7a and 7b. 2. Reference voltage, VREF, is typically at 1/2VCC.
This section describes the basic subsystems and applications of the NE/SA575 Compandor. More theory of operation on compandors can be found in AN174 and AN176. The typical applications of the NE/SA575 low voltage compandor in an Expandor (1:2), Compressor (2:1) and Automatic Level Control (ALC) function are explained. These three circuit configurations are shown in Figures 4, 5 respectively. The NE/SA575 has two channels for a complete companding system. The left channel, A, can be configured a 1:2 Expandor while the right channel, B, can be configured as either a 2:1 Compressor, a 1:2 Expandor or an ALC. Each channel consists of the basic companding building blocks of rectifier cell, variable gain cell, summing amplifier and VREF cell. In addition, the NE/SA575 has two additional high performance uncommitted op amps which can be utilized for application such as filtering, pre-emphasis/de-emphasis or buffering. Figure 6 shows the complete schematic for the applications demo board. Channel A is configured as an expandor while channel B is configured so that it can be used either as a compressor as an ALC circuit. The switch, S1, toggles the circuit between compressor and ALC mode. Jumpers J1 and J2 can be used to either include the additional op amps for signal conditioning or exclude them from the signal path. Bread boarding space is provided for R11, C10 and C11 so that the response can be tailored for each individual need. The components as specified are suitable for the complete audio spectrum from to 20kHz. The most common configuration as a unity gain non-inverting buffer where R10, C10 and C11 are eliminated and R2 and R11 are shorted. Capacitors C5, C8, and C12 are for DC blocking. In systems where the inputs and outputs are AC coupled, these capacitors and resistors can be eliminated. Capacitors C4 and C9 are for setting the attack and release time constant. C6 is for decoupling and stabilizing the voltage reference circuit. The value of C6 should be such that it will offer a very low impedance to the lowest frequencies of interest. Too small a capacitor will allow supply ripple to modulate the audio path. The 1993 Jun 28 1424
better filtered the power supply, the smaller this capacitor can be. R12 provides DC reference voltage to the amplifier of channel B. R6 and R7 provide a DC feedback path for the summing amp of channel B, while is a short-circuit to ground for signals. C14 and C15 are for power supply decoupling. C14 can also be eliminated if the power supply is well regulated with very low noise and ripple.
The applications demo board was built and tested for a frequency range to 20kHz with the component values as shown in Figure 6 and VCC 5V. In the expandor mode, the typical input dynamic range was from to +12dB where 0dB is equal to 100mVRMS. The typical unity gain level measured @ 1kHz input was +0.5dB and the typical tracking error was +0.1dB for input range +10dB. In the compressor mode, the typical input dynamic range was from to +18dB with a tracking error +0.1dB and the typical unity gain level was +0.5dB. In the ALC mode, the typical input dynamic range was from to +8dB with typical output deviation of +0.2dB about the nominal output of 0dB. For input greater than +9dB in ALC configuration, the summing amplifier sometimes exhibits high frequency oscillations. There are several solutions to this problem. The first is to lower the values of R6 and to 20k each. The second is to add a current limiting resistor in series with C12 at Pin 13. The third is to add a compensating capacitor of about to 30pF between the input and output of summing amplifier (Pins 12 and 14). With any one of the above recommendations, the typical ALC mode input range increased to +18dB yielding a dynamic range of over 60dB.
The typical expandor configuration is shown in Figure 3. The variable gain cell and the rectifier cell are in the signal input path. The VREF is always 1/2 VCC to provide the maximum headroom without clipping. The 0dB ref is 100mVRMS. The input is AC coupled through C5, and the output is AC coupled through in a system the inputs and outputs are AC coupled, then C3 and C5 can be eliminated, thus requiring only one external component, C4. The variable gain cell and rectifier cell are DC coupled so any offset
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