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參數(shù)資料
| 型號： | ACE9040 |
| 廠商： | Mitel Networks Corporation |
| 英文描述： | Audio Processor Advance Information |
| 中文描述： | 音頻處理器進展信息 |
| 文件頁數(shù)： | 21/33頁 |
| 文件大?。?/td> | 335K |
| 代理商： | ACE9040 |
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21
ACE9040
TRANSMIT INPUT SIGNAL PRECONDITIONING
Microphone Amplifier (MIG)
Microphone signals input at MI via switch MLI are
amplified by a gain selectable amplifier of either 22 dB or
32 dB, controlled by the MIG bit in the “Handsfree mode”
control message. The microphone amplifier’s input can also
be connected to the line input LI via the MLI switch. The
microphone amplifier’s output drives the soft limiter via switch
MIS which also allows higher level signals from the line input
LI to bypass the microphone amplifier to drive the soft limiter
directly. These two switches are controlled by the MIS and MIL
bits in the “Operation mode” control message.
Soft Limiter
Signal amplitude is restricted without clipping to the
correct level for maximum F.M. deviation by the soft limiter.
This operates as an AGC system, controlled by the signal
amplitude at the compressor input and the hard limiter output
later in the signal processing path. If the signal is too large at
either of these points the soft limiter forward gain is reduced.
The nominal soft limiter gain range of 0 to - 30 dB in 64 steps
of 0·5 dB covers all normal volume changes occuring during
a conversation. Soft limiter attack and decay times are set by
internal clocks derived from SCLK and ramp the gain steps at
nominal rates of one step down every 40
μ
s when the signal
is too large and one step up every 1·68 ms when the signal is
too small.
The soft limiter output at pin SLO is externally coupled
with a capacitor to the input pin IPS of the following gain adjust
stage, INPSENSE. When the speech channel is used to send
DTMF signalling tones a switch, controlled by bit DTMFM in
the “Operation mode” control message, selects the internal
DTMF signal rather than the speech signal at input IPS.
For test purposes TEST[1:0] bits in the “Initializing Mode
1” control message can configure switches to give access to
the softlimiter comparator inputs. When TEST[1:0] bits are
high the 3 & 97 % window comparator is switched from the
hard limiter output to PREIN input and the 92 % comparator is
switched to IPS input.
INPSENSE AMPLIFIER and TXBPF FILTER
Both microphone and transmit voice path tolerances are
trimmed in the INPSENSE gain adjustment block following the
soft limiter and DTMF switch. INPSENSE has a nominal gain
of 8·0 dB with a trim range of - 12·0 to + 12·4 dB relative to the
nominal gain set by bits INPS[4:0] in the “Initializing mode”
control message.
Transmit signal preconditioning is completed by a band-
pass filter TXBPF to limit the audio signal to a speech
bandwidth of 300 Hz to 3·4 kHz. This filter uses switched
capacitor techniques and is preceded by an anti-alias filter and
followed by a smoothing filter to remove the clock from its
output. The typical frequency response is shown in figure 4
which also shows the mask defined by type approval limits.
HANDSFREE FUNCTIONAL BLOCKS
Between the transmit bandpass filter and the compressor
two extra functions are included for use with handsfree
operation. Firstly an attenuator HFGAIN is provided to give
progressive signal reduction in handsfree mode with a range
of 0 to - 49 dB in 7 dB steps, set by bits THF[2:0] in the
“Handsfree mode” control message. The HFGAIN
attenuator’s output drives pin TBPO which is externally
capacitively coupled to the compressor input at pin CIN and
internally drives both the soft limiter and sidetone circuits.
The second function provided for handsfree operation is
a signal rectifier whose output, filtered by an external capacitor
at pin TXC, drives output pin HF via switch HFS with a d.c.
transmit level. Switch HFS is controlled by bit HFS in the
“Handsfree mode” control message. Under control of bit HFS
both receive and transmit levels are available at HF output pin
for external comparison to implement the handsfree function.
The handsfree system is further described in the section
HANDSFREE OPERATION.
COMPRESSOR
ACE9040 provides a 2:1 compressor to halve the transmit
dynamic range as required by analog cellular systems. Within
the operating signal range each 2 dB change in input level
gives a 1 dB change in output level. A transmit signal is input
through pin CIN and output on pin COUT, the signal is
referenced to a mid-supply voltage. CRCIN and CRCOUT are
connections for the external attack and delay time constant
setting components.
The compressor’s nominal unity gain level is 707 mV.
Above this level the signal at CIN is attenuated and below this
level the signal is amplified to achieve the 2:1 dB compression.
Table 20 gives the nominal, Vmax and Vmin levels at CIN and
nominal levels at COUT corresponding with the TACS and
AMPS systems for 0 dB, maximum and minimum deviation.
The gain of the INPSENSE amplifier should be set so that
the compressor operates within these signal levels for a given
input signal at the MIC or LI input.
For the usual attack time of 3·0 ms and decay time of
13·5 ms a 180 k
resistor is connected between CRCIN and
CRCOUT pins and a 100 nF capacitor between CRCIN and
GND pins. An 82 nF capacitor should be connected between
the VMIDTX and GND pins. Attack and decay time is
measured with a 12 dB step, - 8 dB to - 20 dB relative to the
unaffected level. Attack and decay times are respectively
defined at points on the output envelope where it reaches
x 1·5 and x 0·75 of the final steady state level.
External compressor connections allow the use of
external coupling capacitors to remove d.c. offsets and
optionally an external compander. The compressor can be
internally bypassed allowing use of ACE9040 without
companding in non-cellular applications, or for test purposes.
Bits COMP[2:1] in the “Initializing mode 0” control message
control the operation of the internal compander and are used
to switch both the transmit compressor and receive expander
into or out of the signal path. When not in use the internal
compressor and expander are both powered down.
Table 20 Compressor CIN and COUT signal levels for TACS and AMPS
System
Vmax at CIN
Vrms
1.0
1.0
Vmin at CIN
mVrms
1.77
2.25
Nominal Input at CIN
(0dB) levels mVrms
56
71
Nominal Output at COUT
levels mVrms
200
225
dB
+ 25
+ 23
dB
- 30
- 30
TACS
AMPS
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相關(guān)代理商/技術(shù)參數(shù) |
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| ACE9040IGFP1N | 制造商:未知廠家 制造商全稱:未知廠家 功能描述:RF/Baseband Circuit |
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| ACE9040IGFP2R | 制造商:未知廠家 制造商全稱:未知廠家 功能描述:RF/Baseband Circuit |
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