Variable Split Band Inverter
8
MX214/224
Component
Notes
Value
1.0Mꢂ
Selectable
33pF
Tolerance
R1
R2
C1
C2
C3
C4
C5
C6
C7
C8
X1
±10%
±20%
±20%
±20%
±20%
±20%
±20%
±20%
±20%
68pF
15nF
15nF
1
1
1.0µF
1.0µF
1.0µF
1.0µF
1MHz
2
Table 3: Recommended External Components
Notes:
1. C5 and C6 are coupling capacitors between filter outputs and balanced modulator inputs.
2. For best results, a crystal oscillator design should drive the clock inverter input with signal levels of at
least 40% of V , peak to peak. Tuning fork crystals generally cannot meet this requirement. To
DD
obtain crystal oscillator design assistance, consult your crystal manufacturer.
4.
General Description
The MX214/224 Variable Split Band Inverters are designed for mobile and cellular radio voice security
applications. Digital control functions are loaded serially into the MX214. The MX224 is loaded in parallel.
The MX214/224 ICs include a highpass filter that rejects subaudio frequencies, ensuring full CTCSS
compatibility. This CTCSS filter is not included on the earlier generation MX204 VSB Inverter.
The MX214/224 splits the voiceband (300-2700Hz) into upper and lower subbands, and inverts each subband
about itself. The ‘split point’ (defined as the frequency where the voice band is subdivided), is externally
programmable to 32 distinct values in the 300 to 3000Hz range. In the ‘fixed code’ mode, a single point is
used. Fixed mode operation nets approximately 4 mutually exclusive secure channels.
In ‘rolling code’ mode, the split point is changed many times per second, usually under control of a
microprocessor. Rolling code scrambling requires synchronization, offers higher security than fixed code
operation, and provides a much greater number of mutually exclusive secure channels.
The MX214/224 offers a recovered audio product close to that of a telephone. The on-chip ‘ Mute’ function is
useful when implementing rolling code continuous synchronization schemes. ‘Powersave’ and
‘Clear/Scramble’ controls are also included on-chip. Timing and filter clocks are derived internally from an
on-chip 1MHz reference oscillator driven by a 1MHz crystal or clock pulse input.
ꢀ1998 MX-COM, Inc.
4800 Bethania Station Road, Winston-Salem, NC 27105-1201 USA
www.mxcom.com Tel: 800 638 5577 336 744 5050 Fax: 336 744 5054
Doc. # 20480112.002
All trademarks and service marks are held by their respective companies.
CMLMICRO [ CML MICROCIRCUITS ]
