W3030 查看數據表（PDF） - Agere -> LSI Corporation

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W3030

3 V Dual-Mode IF Cellular Receiver

Agere -> LSI Corporation 

W3030 3 V Dual-Mode IF Cellular Receiver

Quadrature Detector (continued)

Data Sheet

April 1999

40 kΩ

dc

QUAD

PIN 3

150 pF

18 pF 4 pF—25 pF 680 µF

R

0.1 µF

Figure 5. L/C Tank Equivalent Circuit

f1= 1 =

1

= 450 kHz

( ) ( ) 2π LC 2π 680 * 6−10 * 184 * 10−12

( ) ( ) ( ) Q = 2π * f * RC = 2π * 450 * 103 * 40 * 103 * 33 * 103 * 184 * 10 −12 = 9.4

( ) 40 * 103 + 33 * 103

Equation (1)

Equation (2)

The W3030 evaluation board is designed with a 450 kHz IF frequency, as shown in our example. The Q of the

tank circuit is set to 10 by the external resistor.

Quad Tank S-Curves

One method of determining if the Q of the tank is too large or too small is to produce an S-curve of the quad

tank. An S-curve is a plot of the dc audio output voltage versus IF input frequency. With small deviations from

center frequency, there is a proportional change in the dc audio output voltage. The overall linearity of the curve

is determined by the Q of the tank circuit; therefore, the Q determines how much deviation is allowed before

distortion of the audio signal occurs. The L/C tank circuit has a shunt resistor to set the Q of the tank. The

procedure to produce these plots is as follows:

1. Remove the 450 kHz IF filter and drive the input of the limiting amplifier with a signal generator capable of

FM modulation.

2. Apply FM modulation and adjust the tank capacitor for maximum audio out and minimal distortion.

3. Remove the FM modulation and sweep the IF frequency above and below center frequency while monitoring

the dc voltage at the audio output.

The following S-curves were produced with the value of the quad tank resistor varied from 18 kΩ, to 30 kΩ, to

removing the resistor. The resistor value of 33 kΩ, which corresponds to a Q of 10, was chosen as the optimal

resistor value.

12

Lucent Technologies Inc.

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