ACE9040 datasheet(26/33 Pages) MITEL

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ACE9040

expander input EIN by using an external summing network

and internally open circuiting the drive to pin RBPO during the

tone (not just muting the speech). This is achieved with bits

COMP[2:1] in the “Initializing mode 0” control message set to

“01”.

Signal dynamic range at input pin EIN is doubled in the 1:2

expander to restore the original signal. Within the operating

signal range each 1 dB change in input level gives a 2 dB

change in output level. The expander output drives pin EOUT

which is coupled by an external capacitor to the input pin

HFGIN. The external connection allows use of an external

compander and removes any d.c. voltage offsets. Bits

COMP[2:1] in the “Initializing mode 0” control message can be

used to select external companding mode and power down

the internal compressor and expander.

The expander’s unity gain level EIN to EOUT is 1V. Above

this level gain is applied to the signal at EIN and below this

level the signal is attenuated to achieve 1:2 dB expansion.

Table 21 gives nominal, Vmax and Vmin levels at EIN and

nominal levels at EOUT corresponding with the TACS and

AMPS systems for 0 dB, maximum and minimum deviation.

The gain of the RXSENSE amplifier should be set so that

the expander operates within these signal levels for a given

demodulated signal range at the RXI input.

Expander pins ERCIN and ERCOUT are used to set the

attack and decay times for the expansion process. For the

usual attack time of 3.0 ms and decay time of 13.5 ms, a

resistor of 180 k

Ω is connected between ERCIN and

ERCOUT pins and a capacitor of 100 nF from ERCIN to GND.

An 82 nF capacitor should be connected between VMIDRX

and GND. Attack and decay time is measured with a 6 dB

step, - 4 dB to - 10 dB relative to the unaffected level. Attack

and decay times are defined respectively at points on the

output envelope where it reaches x 0.57 and x 1.5 of the final

steady state level.

Volume Control and Handsfree Attenuator

Two variable gain stages follow the expander, RXLEVEL

for the volume control and HFATTEN for use with handsfree

mode. Both blocks provide attenuation, expressed as gain to

assist system level design, RXLEVEL from 0 to - 21 dB and

HFATTEN from 0 to - 49 dB. RXLEVEL is controlled by bits

RXV[2:0] in the “Operation mode” control message and

HFATTEN is controlled by bits RHF[2:0] in the “Handsfree

mode” control message.

RX Audio Output: Line Output and Earpiece

Following the handfree attenuator the signal path splits

into two parallel paths: a line output for loudspeaking phones

and drivers for a dynamic earpiece or external handsfree

earpiece. Bits EPH1 and EPH0 in the “Operation Mode” and

“Initializing Mode 0” control messages respectively control the

operation of these outputs, see table 5.

The earpiece output path begins with a variable gain

stage EARSENSE which is controlled by bits EARS[3:0] in the

“Initializing mode 1” control message to give a gain range of -

2·8 to + 3·2 dB. A sidetone signal from the output of the

handsfree attenuator HFGAIN at pin TBPO is added at

EARSENSE's input if bit SD in the “Initializing mode 0” control

message is set to “1”. The output of this block is at pin EAMPI.

The signal at pin EAMPI is amplified by an opamp whose

gain is set by external resistors, allowing overall gain setting

for different models of cellular terminal. A resistor is connected

from EAMPI to the amplifier input pin EAMPFB and a feedback

resistor is connected from the amplifier output EAMPO to

EAMPFB. The ratio of these two resistors sets the gain and the

opamp’s output including feedback resistors should not be

loaded with less than 15 k

Ω. Additional filtering can also be

added to the receive path using the EAMP opamp.

Earpiece

The earpiece drivers have outputs at pins EPOP and

EPON. One of three modes of output drive or a muted output

condition is selected by bits EPH1 and EPH0, see table 5.

A dynamic earpiece, typically of 150

Ω resistance in

series with 800

µH, can be driven when connected between

pin EPON and EPOP. The drive mode can be either differen-

tial (EPH1 = 1, EPH0 = 1) or single ended (EPH1 = 1,

EPH0 = 0). The differential output, drives a minimum of 4 Vpp

into the load. The single ended output appears at EPON and

drives a minimum of 2 Vpp into a load referenced to pin EPOP,

which provides an output voltage at mid-supply.

Output drive is setup for an external handsfree earpiece

with EPH1 = 0 and EPH0 = 1. This load, typically of 64

Ω

resistance in series with 3.3

µF, is driven from pin EPON to

ground and the EPOP output is put into a high impedance

state. The minimum drive into this load is 1.1 Vpp.

The input for the EPOP and EPON output drivers is driven

by the signal at the EAMPO pin for single ended and differen-

tial outputs or from EAMPI directly for a handsfree earpiece,

bypassing the EAMP opamp. The gain from the earpiece

drivers’ common input, to both EPON's inverting and and

EPOP's non-inverting outputs, is nominally + 6 dB.

Line Output

Line output amplifier LODRIVE with its output at pin LO

has a gain of + 5 dB and is used to drive an external audio

power amplifier. LODRIVE can drive a 1 k

Ω load with a

minimum of 1 Vrms. The LO output can be put into a high

impedance state by setting bit HIZ in the “Operation mode”

control message to “0”. During power down EPON and EPOP

and LO are tied to mid-supply voltage.

HANDSFREE OPERATION

In a handsfree telephone the simplest method of prevent-

ing ‘howl round’ caused by acoustic feedback is to attenuate

either the forward or return path until the loop gain is too low

for sustained oscillation. The least active path is attenuated so

the signal level in each path must be detected and compared

so that the quieter can be attenuated.

In the ACE9040 the signal level in both the transmit and

the receive paths are rectified, with smoothing capacitors at

System

Vmax at EIN

Vmin at EIN

Nominal Input at EIN

Nominal Output at EOUT

Vrms

mVrms

(0dB) levels mVrms

levels mVrms

TACS

1.0

+ 12.5

- 15

245

AMPS

1.0

+ 12.3

-21

245

Table 21 Expander EIN and EOUT signal levels for TACS and AMPS

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