MC13158 Ver la hoja de datos (PDF) - Motorola => Freescale

Número de pieza

componentes Descripción

Fabricante

MC13158

WIDEBAND FM IF SUBSYSTEM FOR DECT AND DIGITAL APPLICATIONS

Motorola => Freescale 

Noise

Source

MC13158

Figure 16. System Block Diagram for Noise Analysis

fRF = 112 MHz

LNA

G1 = 18 dB

NF1 = 2.7 dB

SAWF

G2 = 10 dB

NF2 = 10 dB

Mixer fIF = 10.7 MHz

270

330 nH

G3 = 18 dB

47

NF3 = 14 dB

NF

Meter

150 p

Local Oscillator

fLO = 122.7 MHz

Figure 17. 112 MHz LNA

100 n

15 k

3.5 Vdc

510

MPS3906

1.0 k

8.2 k

1.0 k

100 p

RF

Input 100 p 100 nH

680 nH

100 p

FB

100 p

100 nH

RF

Output

MRF941

LOCAL OSCILLATORS

VHF Applications

The on–chip grounded collector transistor may be used for

HF and VHF local oscillator with higher order overtone

crystals. The local oscillator in the application circuit

(Figure 12) shows a 5th overtone oscillator at 122.7 MHz.

This circuit uses a Butler overtone oscillator configuration.

The amplifier is an emitter follower. The crystal is driven from

the emitter and is coupled to the high impedance base

through a capacitive tap network. Operation at the desired

overtone frequency is ensured by the parallel resonant circuit

formed by the variable inductor and the tap capacitors and

parasitic capacitances of the on–chip transistor and PC

board. The variable inductor specified in the schematic could

be replaced with a high tolerance, high Q ceramic or air

wound surface mount component if the other components

have tight enough tolerances. A variable inductor provides an

adjustment for gain and frequency of the resonant tank

ensuring lock up and start–up of the crystal oscillator. The

overtone crystal is chosen with ESR of typically 80 Ω and

120 Ω maximum; if the resistive loss in the crystal is too high

the performance of oscillator may be impacted by lower gain

margins.

A series LC network to ground (which is VCC) is comprised

of the inductance of the base lead of the on–chip transistor

and PC board traces and tap capacitors. Parasitic

oscillations often occur in the 200 to 800 MHz range. A small

resistor is placed in series with the base (Pin 28) to cancel the

negative resistance associated with this undesired mode of

oscillation. Since the base input impedance is so large a

small resistor in the range of 27 to 68 Ω has very little effect

on the desired Butler mode of oscillation.

The crystal parallel capacitance, Co, provides a feedback

path that is low enough in reactance at frequencies of 5th

overtones or higher to cause trouble. Co has little effect near

resonance because of the low impedance of the crystal

motional arm (Rm–Lm–Cm). As the tunable inductor which

forms the resonant tank with the tap capacitors is tuned “off”

the crystal resonant frequency it may be difficult to tell if the

oscillation is under crystal control. Frequency jumps may

occur as the inductor is tuned. In order to eliminate this

behavior an inductor, Lo, is placed in parallel with the crystal.

Lo is chosen to be resonant with the crystal parallel

capacitance, Co, at the desired operation frequency. The

inductor provides a feedback path at frequencies well below

resonance; however, the parallel tank network of the tap

capacitors and tunable inductor prevent oscillation at these

frequencies.

IF Filtering/Matching

In wideband data systems the IF bandpass needed is

greater than can be found in low cost ceramic filters operating

at 10.7 MHz. It is necessary to bandpass limit with LC

networks or series–parallel ceramic filter networks. Murata

offers a series–parallel resonator pair (part number

16

MOTOROLA ANALOG IC DEVICE DATA

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