Preliminary Information
MH88400
R3 1K
C5
22nF
VR
7
C3
Audio Input
0.1µF
RVLC
4
Ring Voltage & Loop
Current Detect Output
RING
VDD
1
+
C1
+5V
AGND
LC
R4
Audio Output
L1
4.7mH
14
13
TIP
R1
1K
C2
D1
10
9
11
TIP
RLS
MH88400
6
VX
TF
TXIN
RING
3
Loop Control Input
2
Meter
Pulse
Detector
Note:
Meter pulses at high frequency (16kHz or 12kHz) and high
level (10V RMS) are used in some countries. The VX
amplifier has a low pass filter which attenuates by typically
15dB at 16kHz. If this proves insufficient for specific applications,
an LC notch is recommended. This should provide
a further 20dB of rejection at 16 of 12kHz with only 0.5dB of loss
at 3.4kHz (after allowing for the overall 6dB loss caused
by R3, R4).
1) R1: 39Ω,1/2W,5%, current
limiting resistor for use in Germany.
2) C1: 10µF, 6V Tantalum
3) C2: 0.1µF, 250V
4) D1: 180VDC Foldback Diode,
e.g. TISP4180, TISP5180.
5) L1: 4.7mH 5%, eg, Siemens B78108-S
6) C5: 22nF 5% for 16kHz 39nF for 12kHz
Figure 6 - Typical Application Circuit with Meter Pulse Filter and Coupling Capacitors
560pF
5%
100k
1%
68k
From
VR
10nF
68k
1%
1%
62k
1%
-
A1
VX Out
5%
-
A1
+
+
100k
100nF
10pF
100k
1%
100k
From
VX
Note:
Amplifier A1 provides a frequency equivalent to the VX path in the MH88400. This
provides the correct phase/amplitude response to enable cancellation to take place in
amplifier A2. Typical THL figures of 15-20dB can be achieved with the values and tolerances
shown. The VR input should be driven from a low impedance < 600R.
This circuit will function correctly for all variants provided the termination impedance of the
external line at the 2W connection is equal to the characteristics impedance of the MH88400.
If it is desired to operate with impedances different from the MH88400 impedances, the
frequency compensation networks around A1 must be filtered. Because of the wide variety
of impedances which are in typical use it is not possible to specify the required values.
0V
Figure 7 -Transhybrid Loss (THL) Cancellation Circuit
2-19
MITEL [ MITEL NETWORKS CORPORATION ]
