|Category||Analog & Mixed-Signal Processing|
|Description||Duplex Frequency Inverter For Cordless Telephones|
|Company||Consumer Microcircuits Limited|
|Datasheet||Download FX118DW/P datasheet
Features/Applications Frequency Inversion Scrambling Full-Duplex Operation High Baseband and Carrier Rejection Audio Lowpass and Bandpass Filtering On-Chip Xtal Oscillator Stabilty
Low Power Requirement (3.0 Volt Minimum) Cordless Telephones Base and Handheld Applications Input Gain Adjustment Plastic DIL and S.O.I.C. Package Styles
The is a low-power, full-duplex frequency inverter available to provide voice privacy for cordless telephone systems by mixing the incoming audio with an internally produced carrier frequency (3.3kHz). This chip contains two completely separate audio channels (C1 and C2) each comprising a "componentadjustable" input amplifier, a 10th-order lowpass filter, a balanced modulator and a 14th-order bandpass filter output. The on-chip modulation process has the properties of high baseband and carrier frequency rejection which when combined with high-order output filtering, produces a high-quality recovered voiceband audio.
The frequency stability of the FX118 is achieved by an on-chip oscillator employing an external 4.433619MHz Xtal or clock input to produce the common carrier frequency and the sampling clocks for the switched capacitor low and bandpass filters. This microcircuit has a low power requirement of 3.0 volts (min.) and is encapsulated in either 16-pin DIL or small outline SMD (S.O.I.C.) plastic packages both of which are of a physical size suitable for either base or handset type telephone instruments as well as batteryportable and mobile communications systems.
No Internal Connection: It is recommended that, to improve noise conditions, this pin is connected to VSS.
LPF(1) Out: The output of the Channel 1 Lowpass Filter. to be coupled "B Mod(1) In" via a 1.0µF capacitor see Figure 2.
B Mod(1) In: The input to Channel 1 balanced modulator. Internally biased to be coupled to "LPF(1)" via a 1.0µF capacitor see Figure 2.
C1 Amp Output: Channel 1 amplifier with external components (see Figure 2) can be used to provide gain in the signal path.
C1 In: The negative input of Channel 1 Amplifier. Recommended external components are shown in Figure 2.
C2 In: The negative input of Channel 2 Amplifier. Recommended external components are shown in Figure 2.
C2 Amp Output: Channel 2 amplifier with external components (see Figure 2) can be used to provide gain in the signal path.
VBIAS: The internal analogue bias line VDD/2. It should be decoupled to VSS via 1.0µF or greater capacitor. See Figure 2.
B Mod(2) In: The input to Channel 2 balanced modulator. Internally biased to be coupled to "LPF(2)" via a 1.0µF capacitor see Figure 2.
LPF(2) Out: The output of the Channel 2 Lowpass Filter. to be coupled "B Mod(2) In" via a 1.0µF capacitor see Figure 2.
VDD: The positive supply rail. A single positive supply voltage 5.0v) is required. Levels and voltages within the Duplex Frequency Inverter are dependent upon this supply.
Xtal/Clock: 4.433619 MHz Xtal or externally derived clock is injected at this pin. See Figure 2. Operation of the FX118 without a Xtal or clock input may cause device damage.
1. Configurations R3, C5 and R5, C6 should be chosen with respect to the specific application. 2. Operation of any CML microcircuit without a Xtal or clock input may cause device damage. To minimise damage in the event of a Xtal/drive failure, it is recommended that the power rail (VDD) is fitted with a current limiting device (resistor or fast-reaction fuse).FM CHANNEL (C1) RF AMP PREEMPHASIS CHANNEL (C2) FM HYBRID TRANSFORMER AF AMP TELEPHONE LINE
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