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PDF AS2520T Data sheet ( Hoja de datos )
| Número de pieza | AS2520T | |
| Descripción | Telephone Speech Circuit with Loudhearing and Handsfree | |
| Fabricantes | austriamicrosystems AG | |
| Logotipo |  |
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Preliminary
AS2520/21/20B/21B
Telephone Speech Circuit
with Loudhearing and Handsfree
Austria Mikro Systeme International AG
Key Features
u Line/speech circuit, loudhearing, handsfree and
dc/dc converter on one 28 pin CMOS chip
u Operating range from 13 to 100 mA (down to 5
mA with reduced performance)
u Soft clipping control eliminating harsh distortion
u Volume control of receive signal with squelch and
automatic loop gain compensation
u Line loss compensation pin selectable
u Low noise (max. - 72 dBmp)
u Real or complex impedance adjustable
u NET 4 compatible
u Dynamically controlled voice switching
u Same monitor amplifier for loudhearing, handsfree
and tone ringer
u Very few external components
u Power derived from ring signal by switching
converter during ringing
Typical Application
La
General Description
The AS2520/21/20B/21B are CMOS integrated
circuits that contain all the audio functions needed to
form a high comfort, line-powered telephone.
The devices incorporate line adaptation, speech
circuit, loudhearing and handsfree - all supervised by
the novel voice and power control circuit. A switching
converter is also provided for converting the ring
signal. The interface to a dialler/controller is made
very simple to allow easy adaptation to a telecom
microcontroller.
The AS2520 series incorporate volume control for the
earpiece and the loudspeaker (AS2520 digital with +/-
keys and AS2521 analogue with potentiometer). The
volume control circuit automatically compensates the
loop gain to ensure acoustic stability.
Package
Available in 28 pin SOP and DIP.
Lb
3V
123
456
789
*0 #
DIALLER
µCONTROLLER
LCD DRIVER
TELEPHONE
SPEECH CIRCUIT
WITH
LOUDHEARING,
HANDSFREE,
DC/DC CONVERTER
HSM
HFM
Rev. 5.1
AS2520
Figure 1: Typical Handsfree Telephone Application
Page 1
May 1999
1 page  
Preliminary
AS2520/21/20B/21B
DC Conditions
The normal operating range (off-hook) is from 13 mA
to 100 mA. Operating range with reduced
performance is from 5 mA to 13 mA (parallel
operation). In the normal operating range all
functions are operational.
In the line hold range from 0 to 5 mA the device is in
a power down mode and the voltage at LI is reduced
to maximum 3.5V.
The dc characteristic (excluding diode bridge) is
determined by the voltage at LI and the resistor R1 at
line currents above 13 mA as follows:
VLS = VLI + ILINE ž R1
The voltage at LI is 4.5V.
Below 13 mA the AS252x provides an additional
slope in order to allow parallel operation (see figure
3).
8
(V)
7
VLS
6
5
4 VLI
3 Typically
No ac signals
2 Tamb: 25°C
1
0
0 10 20 30 40 50 60 70 80 90 100
Line Current
(mA)
(see application notes). The dc resistance of R1
should be kept at 30 ohm to ensure correct dc
condition.
Return loss and sidetone cancellation can be
determined independent of each other (see figure 4).
Speech Circuit
The speech circuit consists of a transmit and a
receive path with soft clipping, mute, line loss
compensation and sidetone cancellation.
Transmit
The gain of the transmit path is 36.5 dB in handset
mode (from M1/M2 to LS) and 46.5 dB in handsfree
mode (from M3/M4 to LS). The microphone inputs
have an input impedance of 15 kohm.
The unique dual soft clipping control circuit limits the
output voltage at LI to 2V .PEAK Dual means that the soft
clipping incorporates both a very fast control circuit to
eliminate harsh sidetone distortion and a slower
regulation circuit to limit the output voltage at 2VPEAK
independent of the line impedance. The attack time
is 30 µs/6 dB. The overdrive range is 30 dB. When
mute is active, pin MT high, the gain is reduced by >
60 dB.
Receive
The gain of the receive path is 3 dB (test circuit
figure 8) from RI to RO. The receive input is the
differential signal of RI and STB. Also the receive
channel provides soft clipping to avoid acoustic
shock and harsh distortion.
Figure 3: DC Mask
When the PD pin is high (during pulse dialling) the
speech circuit and other part of the device not
operating are in a power down mode to save current.
The CS pin is pulled to V in order to turn the
SS
external shunt transistor on to keep a low voltage
drop at the LS pin during make periods.
AC Impedance
The synthesised ac impedance of the circuit is set on
chip and by an external resistor and an external
capacitor (for complex impedance).
When mute is active during dialling the gain is
reduced by > 60 dB. During DTMF dialling a MF
comfort tone is applied to the receiver. The comfort
tone is the DTMF signal with a level that is -30 dB
relative to the line signal.
Volume Control
On the AS2520 the receive gain can be changed by
pressing the volume keys. The + key increases the
gain by 10 dB in 5 steps and the – key decreases the
gain by 10 dB in 5 steps. The gain is reset by next
off-hook. The volume can also be controlled via a
microcontroller.
When R1 is set to 30 ohm, the ac impedance is 1000
ohm real, and the complex part can be set by a
capacitor connected to pin 2 (CI).
The AS2521 uses a potentiometer to control the
receive gain. The volume is an indirect dc control to
avoid that noise is introduced from the potentiometer.
For 600 ohm telephones it is recommended to
connect a resistor and a capacitor from pin LS to V
SS
The volume control is common for both the earpiece
and the loudspeaker. Any increase will be
compensated to ensure acoustic stability.
Rev. 5.1
Page 5
May 1999
5 Page 
Preliminary
Receive
Symbol Parameter
ARX Gain (LS to RO), Default
LSP Gain (LSI to LO)
∆ATX/F
ALLC
ARX
THD
Variation with Frequency
Gain Range, LLC
Volume Range
Distortion
VSC Soft Clip Level (RO)
Soft Clip Level (LO)
Condition
Volume reset
f = 500 Hz to 3.4 kHz
Speech mode; LLC = VSS or VDD
10 steps, each 2 dB
VRI < 0.2 VRMS
VRO =
Not AS2520B/21B; VLO =
Unloaded
Min.
1.5
17.5
AS2520/21/20B/21B
Typ.
3
19
+/- 0.8
-6
20
1
1.3
Max. Units
4.5 dB
20.5 dB
dB
dB
dB
2%
VPEAK
VPEAK
ASCO
VRTH
AAD
tDECAY
tDECAY
VNO
VUFC
ZIN
VIN RI
AST
ZIN
VIN ST
Soft Clip Overdrive
30 dB
Threshold Voltage at RTH
7 15 25 mV
Attenuation Depth
30 dB
Attack Time
Decay Time
Channel control; VRI > 0.8 VRMS
Channel control
µs/6dB
µs/6dB
Noise Output Voltage (RO) HS = high; TAMB = 25°C
Unwanted Frequency
Components (RO)
50 Hz.........20 kHz
-72 dBmp
-60 dBmp
Input Impedance, RI
8 kohm
Input Voltage Range, RI
Sidetone Cancellation
Input Impedance, STB
VRI < 0.2 VRMS; TAMB = 25°C
+/- 2
26
80
VPEAK
dB
kohm
Input Voltage Range, STB
+/- 2
VPEAK
General Timings
Symbol Parameter
Condition
tVOL Volume Key Debounce
tSCA
Soft Clip Attack Time
VIN above soft clip level
tSCD
Soft Clip Decay Time
VIN below soft clip level
tPDA Peak Detector Attack Time VIN above VTH
tPDD Peak Detector Decay Time VIN below VTH
tLPA Low-Power Attack Time VPP < 3.6V
tLPD
Low-Power Release
VPP > 3.6V
Min.
Typ.
7
0.12
128
3.2
29
250
1
Max. Units
ms
ms/6dB
ms/6dB
ms/V
ms/V
ms/6dB
sec/6dB
Rev. 5.1
Page 11
May 1999
11 Page | ||
| Páginas | Total 14 Páginas | |
| PDF Descargar | [ Datasheet AS2520T.PDF ] | |
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