NE570

INTEGRATED CIRCUITS NE570 Compandor Product data Supersedes data of 1990 Jun 07 2003 Apr 03 Philips Semiconductors Philips Semiconductors Product data Compandor NE570 GENERAL DESCRIPTION The NE570 is a versatile low cost dual gain control circuit in which either channel may be used as a dynamic range compressor or expandor. Each channel has a full-wave rectifier to detect the average value of the signal, a linerarized temperature-compensated variable gain cell, and an operational amplifier. The NE570 is well suited for use in cellular radio and radio communications systems, modems, telephone, and satellite broadcast/receive audio systems. PIN CONFIGURATION RECT_CAP_1 RECT_IN_1 ∆G_CELL_IN_1 GND INV_IN_1 RES_R3_1 1 2 3 4 5 6 7 8 TOP VIEW 16 15 14 13 RECT_CAP_2 RECT_IN_2 ∆G_CELL_IN_2 VCC INV_IN_2 RES_R3_2 OUTPUT_2 THD_TRIM_2 NE570D 12 11 10 9 FEATURES OUTPUT_1 THD_TRIM_1 • Complete compressor and expandor in one IC • Temperature compensated • Greater than 110 dB dynamic range • Operates down to 6 VDC • System levels adjustable with external components • Distortion may be trimmed out APPLICATIONS SR02503 Figure 1. Pin configuration. • Cellular radio • Telephone trunk comandor • High level limiter • Low level expandor—noise gate • Dynamic noise reduction systems • Voltage-controlled amplifier • Dynamic filters ORDERING INFORMATION Type number Package Name NE570D SO16 Description plastic small outline package; 16 leads; body width 7.5 mm Version SOT162-1 0 °C to +70 °C Temperature range BLOCK DIAGRAM THD TRIM R3 R3 20 kΩ VARIABLE GAIN R4 30 kΩ R1 10 kΩ RECT IN RECTIFIER VREF 1.8 V – OUTPUT + INVERTER IN ∆G CELL IN R2 20 kΩ RECT CAP SR02507 Figure 2. Block diagram 2003 Apr 03 2 Philips Semiconductors Product data Compandor NE570 ABSOLUTE MAXIMUM RATINGS SYMBOL VCC Tamb PD Maximum operating voltage Operating ambient temperature range Power dissipation PARAMETER RATING 24 0 to +70 400 UNITS VDC °C mW AC ELECTRICAL CHARACTERISTICS VCC = +6 V, Tamb = 25 °C; unless otherwise stated. LIMITS SYMBOL VCC ICC IOUT SR PARAMETER Supply voltage Supply current Output current capability Output slew rate Gain cell distortion 2 Untrimmed Trimmed Resistor tolerance Internal reference voltage Output DC shift 3 Expandor output noise Unity gain level5 Gain change 2, 4 Reference drift 4 Resistor drift 4 Tracking error (measured relative to value error (measured relative to value at unity gain) equals [VO – VO (unity gain)] dB – V2 dBm dB Channel separation NOTES: 1. Input to V1 and V2 grounded. 2. Measured at 0 dBm, 1 kHz. 3. Expandor AC input change from no signal to 0 dBm. 4. Relative to value at Tamb = 25 °C. 5. 0 dB = 775 mVRMS. Tamb = 0 °C to +70 °C Tamb = 0 °C to +70 °C Tamb = 0 °C to +70 °C Rectifier input V2 = +6 dBm, V1 = 0 dB V2 = -30dBm, V1 = 0dB – – – ±0.2 +0.2 60 – –0.5, +1 – dB dB dB Untrimmed No signal, 15 Hz to 20 kHz 1 No signal TEST CONDITIONS CONDITIONS MIN 6 – ±20 – – – – 1.7 – – –1 – – – TYP – 3.2 – ±0.5 0.3 0.05 ±5 1.8 ±20 20 0 ±0.1 ±5 +1, –0 MAX 24 4.8 – – 1.0 – ±15 1.9 ±100 45 +1 ±0.2 ±10 – UNITS V mA mA V/µs % % % V mV µV dBm dB mV % 2003 Apr 03 3 Philips Semiconductors Product data Compandor NE570 CIRCUIT DESCRIPTION The NE570 compandor building blocks, as shown in the block diagram, are a full-wave rectifier, a variable gain cell, an operational amplifier and a bias system. The arrangement of these blocks in the IC result in a circuit which can perform well with few external components, yet can be adapted to many diverse applications. The full-wave rectifier rectifies the input current which flows from the rectifier input, to an internal summing node which is biased at VREF. The rectified current is averaged on an external filter capacitor tied to the CRECT terminal, and the average value of the input current controls the gain of the variable gain cell. The gain will thus be proportional to the average value of the input signal for capacitively-coupled voltage inputs as shown in the following equation. Note that for capacitively-coupled inputs there is no offset voltage capable of producing a gain error. The only error will come from the bias current of the rectifier (supplied internally) which is less than 0.1 µA. |V IN * V REF | avg GT R1 or | V IN | avg GT R1 The speed with which gain changes to follow changes in input signal levels is determined by the rectifier filter capacitor. A small capacitor will yield rapid response but will not fully filter low frequency signals. Any ripple on the gain control signal will modulate the signal passing through the variable gain cell. In an expander or compressor application, this would lead to third harmonic distortion, so there is a trade-off to be made between fast attack and decay times and distortion. For step changes in amplitude, the change in gain with time is shown by this equation. G(t) + (G initial * G final) e * t t ) G final ; t + 10k C RECT The variable gain cell is a current-in, current-out device with the ratio IOUT/IIN controlled by the rectifier. IIN is the current which flows from the ∆G input to an internal summing node biased at VREF. The following equation applies for capacitively-coupled inputs. The output current, IOUT, is fed to the summing node of the op amp. V IN * V REF V IN + I IN + R2 R2 A compensation scheme built into the ∆G cell compensates for temperature and cancels out odd harmonic distortion. The only distortion which remains is even harmonics, and they exist only because of internal offset voltages. The THD trim terminal provides a means for nulling the internal offsets for low distortion operation. The operational amplifier (which is internally compensated) has the non-inverting input tied to VREF, and the inverting input connected to the ∆G cell output as well as brought out externally. A resistor, R3, is brought out from the summing node and allows compressor or expander gain to be determined only by internal components. The output stage is capable of ±20 mA output current. This allows a +13 dBm (3.5 VRMS) output into a 300 Ω load which, with a series resistor and proper transformer, can result in +13 dBm with a 600 Ω output impedance. A bandgap reference provides the reference voltage for all summing nodes, a regulated supply voltage for the rectifier and ∆G cell, and a bias current for the ∆G cell. The low tempco of this type of reference provides very stable biasing over a wide temperature range. The typical performance characteristics illustration shows the basic input-output transfer curve for basic compressor or expander circuits. COMPRESSOR INPUT LEVEL OR EXPANDOR OUTPUT LEVEL (dBm) +20 +10 0 –10 –20 –30 –40 –50 –60 –70 –80 –40 –30 –20 –10 0 +10 COMPRESSOR OUTPUT LEVEL OR EXPANDOR INPUT LEVEL (dBm) SR00677 Figure 3. Basic input-output transfer curve TYPICAL TEST CIRCUIT VCC = 15 V 0.1 µF 13 10 µF 6, 11 20 kΩ V1 3, 14 2.2 µF 20 kΩ ∆G – + 7, 10 VO VREF 2, 15 V2 2.2 µF 10 kΩ 30 kΩ 4 1, 16 2.2 µF 5, 12 8.2 kΩ 8, 9 200 pF SR02508 Figure 4. Typical Test Circuit 2003 Apr 03 4 Philips Semiconductors Product data Compandor NE570 INTRODUCTION Much interest has been expressed in high performance electronic gain control circuits. For non-critical applications, an integrated circuit operational transconductance amplifier can be used, but when high-performance is required, one has to resort to complex discrete circuitry with many expensive, well-matched components. This paper describes an inexpensive integrated circuit, the NE570 Compandor, which offers a pair of high performance gain control circuits featuring low distortion (