– 5-12 –
■
AFC Control
The Automatic Frequency Control (AFC) Unit generates a pulse number modulated (PNM) signal which can be low pass
filtered externally to make a programmable DC voltage for controlling the external VCXO. The PNM signal repeats itself with
a period depending on the number of bits used in register AFCVAL.
For standard applications, the upper 11 bits are used and the PNM signal repeats every 2048 13 MHz clock cycles.
(Approx. 158
µ
sec, frequency 6.35 kHz) For each 13 MHz clock input to the block, the output is driven to "1" or "0".
The ratio of the number of "1"s to "0"s output in a period is proportional to the value of the AFCVAL register. The "1"s are
distributed equally in a PNM period. No pulse deviates more from a perfect distribution by more than 1 input clock period. For
instance if the value 7 is programmed, the leading edge of the seven 77 nsec wide pulses are separated by 293, 293, 292,
293, 292, 293 and 292 clock periods, which is near the ideal value of 292.57. The equal spacing in a period ensures that most
of the energy in the signal appears at harmonics of 6.35 kHz, (in this case 7 x 6.35 kHz), and very little at 6.35 kHz. Because
of this the requirements for the low pass filter are considerably reduced compared to a pulse width modulated output or a
pulse number modulated signal with unequal distribution. In this example which uses 11-bits, the lowest frequency component
in the spectrum of any E-Gold + V3 PNM sequence is 6.35 kHz and has an effective amplitude of less than 1 LSB.
■
Audio
E-Gold + V3 provides the analogue interface for the digital audio samples processed by the DSP in E-Gold + V3.
Voice Uplink and Downlink path
■
Auxiliary A/D
U2001 (E-Gold + V3) provides 5-input 10-bit A/D converters for monitoring. These inputs are available externally to monitor the
main battery voltage, charger voltage and charger current monitoring.
The functions of the four external A/D inputs are as follows.
Figure 5.6. Voice ADC and DAC block diagram
E-Gold+ V3 A/D inputs
E-Gold + input
Pin No.
Function
Values
VBAT
P1
Battery voltage
TBAT
P2
Battery Temperature
TENV
P3
Environment Temperature
TVCO
H1
Quartz Temperature
No connection in EB-X400
BTEC
N2
Battery technology identification
No connection in EB-X400
1
2
2
MUX
VOICEBAND-SAMPLE-BUFFER
ADC
DAC
Scal_In
Scal_Mic
Speech
_Mix
Side_
Tone
Gain_
Out
Biquad-
In #1
Tone
Generator
#2
Tone_
Mix
Biquad-
In #2
Scal_
Out
Scal_
Rec
Biquad-
In #1
Truncation
to 16 bits
Biquad-
In #2
Tone
Generator
#3
Tone
Generator
#1
1
a0
a2
2
∗
a1
b2
2
∗
b1
T
T
T
T
Biquad-Filter
Input
Output
Содержание EB-X400
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