ACE9040 datasheet(25/33 Pages) MITEL

25 / 33 page

ACE9040

RECEIVE VOICE PATH

Fig. 15 Receive Voice Path

De-emphasis and Receive Signal Input

Demodulated FM signals drive the RXI input pin via an

external de-emphasis lowpass R-C filter of typically 180 k

Ω

and 10 nF. With TONEM switch set to RXI the input signal is

amplified in the block RXSENSE with a gain of + 8 dB.

RXSENSE also provides fine adjustment over a range of

- 6·0 dB to + 6·4 dB to take up signal level tolerances in the

receiver output. Fine gain adjustment is controlled by

RXSEN[4:0] bits in the “Initializing mode 0” control message.

When the DTMF generator in the transmit section is in use

its output can be switched into the receive path to replace the

RXI signal by setting bit TONEM in the “Operation mode”

control message to “1”. This does not affect the transmitted

signal but allows the user to hear DTMF tones to confirm key

press operation.

RX Bandpass Filter

The RXSENSE amplifier’s output is bandpass filtered to

the speech bandwidth of 300 to 3400 Hz by receive bandpass

filter RXBPF, as shown in figure 7. RXBPF uses switched

capacitor filter techniques but does not include an anti-alias

input filter as signals at RXI from the external receiver’s output

and the internal DTMF generator’s output are already

bandlimited. The F.M. discriminator output signals from

ACE9040’s companion device “ACE9030: Radio Interface

and Twin Synthesiser” are bandlimited by its output filter and

ACE9040’s internal DTMF tones are generated as sinewaves

without the need for a further anti-aliasing filiter.

RXBPF filter output passes through the receive mute

switch controlled by bit RXM in the “Operation mode” control

message and is buffered to drive pin RBPO by amplifier

EXPGAIN. During mute the RBPO pin is driven to the signal

ground voltage at mid supply (as found on pin BIAS).

EXPGAIN gain is nominally 12.3 dB when using the internal

expander and 0 dB when using an external expander. The

output circuit driving RBPO includes a smoothing filter to

remove clock noise.

Expander

Input to the expander at pin EIN is coupled by an external

capacitor from RBPO to remove any d.c. voltage offsets.

Using external coupling also allows the option of using an

external compander or bypassing the expander if a linear

system is required. In either case the signal should feed back

into ACE9040 at pin HFGIN. ACE9040’s compander can be

bypassed by setting bits COMP[2:1] in the “Initializing mode 0”

control message to “00”.

A ring tone from the BAR (Beep, Alarm, Ring) generator

of ACE9050 “System Controller” can be added to the

EPOP

EPON

150W

64W

3.3

µF

EARPIECE

DRIVER

+ 6dB

EPH0/EPH1

EAMPO

HFGIN

10nF

EOUT

82nF

100nF

180k

Ω

ERCIN

ERCOUT

EIN

RBPO

33nF

1dB to 2dB

12.3dB

EXPGAIN

+5dB

HIZ

LODRIVE

0dB

RXBPF

DTMF INPUT

RXSENSE

8dB

-6.4 to 6.4dB

RXM

SIDETONE

INPUT (-19dB)

TONEM

RXI

180k

Ω

10nF

NOM -12dB

-21 to 0dB

0 to-49dB

RXLEVEL

HFATTEN

HANDSFREEE

RECTIFIER

-2.8 to + 3.2

EARSENSE

TXC

HFS

RXC

68nF

EAMPI

EAMP

EAMPFB

VMID

EPH0/EHP1

EXPANDER

VMIDRX

COMP[2:1]

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