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Fabricante

ML13156

Wideband FM IF System

LANSDALE Semiconductor Inc. 

ML13156

LANSDALE Semiconductor, Inc.

Legacy Applications Information

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 24) 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 overtone 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 capaci-

tors 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 behav-

ior an inductor (Lo) is placed in parallel with the crystal. Lo is cho-

sen to 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 net-

work of the tap capacitors and tunable inductor prevent oscillation

at these frequencies.

The input matching network uses a 1:4 impedance matching trans-

former (Recommended sources are Mini–Circuits and Coilcraft).

Using the same IF ceramic filters and quadrature detector circuit as

specified in the applications circuit in Figure 17, the 12 dB SINAD

performance is –95 dBm for a fmod = 1.0 kHz sinusoidal wave-

form and fdev ±40 kHz.

This circuit is breadboarded using the evaluation PC bard shown in

Figures 32 and 33. The RF ground is VCC and path lengths are

minimized. High quality surface mount components were used

except where specified. The absolute values of the components

used will vary with layout placement and component parasitics.

RSSI RESPONSE

Figure 24 shows the full RSSI response in the application circuit.

The 10.7 MHz, 110 kHz wide bandpass ceramic filters (recom-

mended sources are TOKO part # SK107M5–AO–10X or Murata

Erie SFE10.7MHY–A) provide the correct band pass insertion loss

to linearize the curve between the limiter and IF portions of RSSI.

Figure 23 shows that limiting occurs at an input of –100 dBm. As

shown in Figure 24, the RSSI output linear from –100 dBm to –30

dBm.

UHF APPLICATION

Figure 20 shows a 318.5 to 320 MHz receiver which drives the

mixer with an external varactor controlled (307.8 to 309.3 MHz)

LC oscillator using an MPS901 (RF low power transistor in a

TO–92 plastic package; also MMBR901 is available in a SOT–23

surface mount package). With the 50 kΩ 10 turn potentiomenter

this oscillator is tunable over a range of approximately 1.5 MHz.

The MMBV909L is a low voltage varactor suitable for UHF appli-

cations; it is a dual back–to–back varactor in a SOT–23 package.

The RSSI rise and fall times for various RF input signal levels and

R20 values are measures at Pin 20 without 10 nF filter capacitor. A

10 kHz square wave pulses the RF input signal on and off. Figure

25 shows that the rise and fall times are short enough to recover

greater than 10 kHz ASK data; with a wider IF band pass filters

data rates up to 50 kHz may be achieved. The circuit used is the

application circuit in Figure 17 with no RSSI output filter capacitor.

Figure 18. MC13156DW Application Circuit

fRF = 104 MHz; fLO = 93.30 MHz

5th Overtone Crystal Oscillator

33

(4)

0.135 µH

+1.0 µ

104 MHz

(2)

10 p

RF Input

SMA 3.0 p

120 p

1

(1)

0.1 µ

2

10 n

3

To Filter

Mixer

27 p

24

1.0 µH

(3)

30 p

23

4.7 k 5th OT

XTAL

VEE 22

10 n

VCC

Page 14 of 21

NOTES: 1. 0.1 µH Variable Shielded Inductor: Coilcraft part # M1283–A or equivalent.

2. Capacitors are Silver Mica.

3. 5th Overtone, Series Resonant, 25 PPM Crystal at 93.300 MHz.

4. 0.135 µH Variable Shielded Inductor: Coilcraft part # 146–05J08S or equivalent.

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