ucb1100 NXP Semiconductors, ucb1100 Datasheet - Page 9

• Manufacturer Part Number: ucb1100
• Description: Advanced Modem/audio Analog Front-end
• Manufacturer: NXP Semiconductors

Philips Semiconductors
The UCB1100 audio codec input path accepts microphone signals
directly, only a DC blocking capacitor is needed, since the micp input
is biased around 1.4V. The ‘ground’ side of the microphone is either
connected to the analogue ground (vssa1) or to the micgnd pin of
the UCB1100. The latter will decrease the current consumption of
active microphones, since the micgnd pin is made Hi-Z when the
audio codec input path is disabled.
The full scale input voltage of the audio input path is programmable
in 1.5dB steps by setting the appropriate data in the audio-input-gain
bits in the audio control register A.
A clip detection circuit will inform the user whenever the input
voltage exceeds the maximum input voltage. In that case the clip
detect status bit in audio control register B is set. An interrupt is
generated on the irqout pin of the UCB1100 whenever the enable
audio clip detect rising interrupt or the enable audio detect falling
edge interrupt bit is set in the rising edge interrupt enable or falling
edge interrupt control register B is set.
1998 May 08
Advanced modem/audio analog front-end
‘Passive’ Microphone
Figure 5. Analogue and Digital Attenuation Settings
48dB
24dB
21dB
0dB
0dB
Figure 4. Possible Microphone Connections
micgnd
vssa1
vdda1
micp
UCB1100
Audio Output Path
24dB
programmed attenuation
‘Active’ Microphone
48dB
micgnd
vssa1
vdda1
micp
UCB1100
SN00129
SN00130
69dB
9
The output level can be attenuated in 3dB steps down to -69dB. The
8 highest attenuation steps are implemented in the analogue
circuitry, while the two 24dB steps are implemented in the digital
domain. This preserves the ‘audio quality’ of the output signal at
lowest attenuation settings. The speaker driver is muted when the
audio-mute bit in the audio control register B is set. The speaker
driver will remain activated in that case, however no signal is
produced by the speaker driver circuitry.
The speaker driver is designed to directly drive a bridge tied load
(BTL). This yields the highest output power and it does not require
external DC blocking capacitors. The speaker driver also accepts
single ended connection of a speaker, in which case the maximum
output power is reduced to a quarter of the BTL situation.
Consequently this way of connecting the speaker to the speaker
driver reduces the power consumption of the speaker driver in the
UCB1100 by a factor of 2. Figure 6 shows possible ways to connect
a speaker to the UCB1100.
The audio input and output path are activated independently; the
input path is enabled when the audio-input-enable bit is set, the
output path is enabled when the audio-output-enable bit is set in the
audio control register B. This provides the user the means to reduce
the current consumption of the UCB1100 if one part of the audio
codec is not used in the application.
The audio codec has a loopback mode for system test purposes,
which is activated when the audio_loopback enable bit in the audio
control register B is set. This is an analogue loopback which
internally connects the output of the audio output path to the input of
the audio input path, (see Figure 3). In this mode the normal
microphone input is ignored, but the speaker driver can be operated
normally.
Bridge Tied
Speaker
UCB1100
Load
spkrp
spkrn
Figure 6. Possible Speaker Connections
UCB1100
Single Ended Speaker Connections
spkrp
spkrn
UCB1100
Preliminary specification
UCB1100
spkrp
spkrn
SN00131