Philips Semiconductors

Product specification

SA625

High performance low power mixer FM IF system

with high-speed RSSI

1997 Nov 07

8

RF GENERATOR

NE625 DEMO BOARD

RSSI

AUDIO

DATA

C–MESSAGE

HP339A DISTORTION

ANALYZER

SCOPE

DC VOLTMETER

45MHz

SR00460

Figure 5. SA625 Application Circuit Test Set Up

NOTES:

1. C-message: The C-message filter has a peak gain of 100 for accurate measurements. Without the gain, the measurements may be

affected by the noise of the scope and HP339 analyzer.

2. Ceramic filters: The ceramic filters can be 30kHz SFG455A3s made by Murata which have 30kHz IF bandwidth (they come in blue), or

16kHz CFU455Ds, also made by Murata (they come in black). All of our specifications and testing are done with the more wideband filter.

3. RF generator: Set your RF generator at 45.000MHz, use a 1kHz modulation frequency and a 6kHz deviation if you use 16kHz filters, or

8kHz if you use 30kHz filters.

4. Sensitivity: The measured typical sensitivity for 12dB SINAD should be 0.22

µV or -120dBm at the RF input.

5. Layout: The layout is very critical in the performance of the receiver. We highly recommend our demo board layout.

6. RSSI: The smallest RSSI voltage (i.e., when no RF input is present and the input is terminated) is a measure of the quality of the layout and

design. If the lowest RSSI voltage is 250mV or higher, it means the receiver is in regenerative mode. In that case, the receiver sensitivity

will be worse than expected.

7. Supply bypass and shielding: All of the inductors, the quad tank, and their shield must be grounded. A 10-15

µF or higher value tantalum

capacitor on the supply line is essential. A low frequency ESR screening test on this capacitor will ensure consistent good sensitivity in

production. A 0.1

µF bypass capacitor on the supply pin, and grounded near the 44.545MHz oscillator improves sensitivity by 2-3dB.

8. R5 can be used to bias the oscillator transistor at a higher current for operation above 45MHz. Recommended value is 22k

Ω, but should not

be below 10k

Ω.