SAW Transmit Band Pass Filter | Ericsson LPE-200 guide

AE/LZB 119 1902 R1A

(MODQ and MODQ_B). The I input passes through a low pass filter consisting of capacitors C191, C192 and C193, resistor R166 and inductors L156 and L157. The output of this filter connects to N150, Pins 43 (I) and 42 (I_bar). The Q input passes through a low pass filter consisting of capacitors C194, C195 and C196, resistor R167 and inductor L158 and L159. The output of this low pass filter connects to N150, Pins 41 (Q) and 40 (Q_bar). The I and Q inputs are summed with the lower side band then the outputs of these mixer circuits are summed to produce the lower side band with transmit modulation. This signal is amplified and connected through N150, Pin 34 (DUAL TX) to the input of a transmit band pass filter.

SAW Transmit Band Pass Filter 1

The TX_RF signal (0 dBm) connects through coupling capacitor C125 to the input of a TX Band Pass Filter. Filtering of the TX_RF line is provided by capacitor C126. The lower sideband output of the band pass filter (-8 dB) connects through coupling capacitors C121 and C139 to the base of buffer amplifier transistor V104. Filtering is provided by capacitor C120.

Directional Coupler (W100)

The RF output connected to W100, Pin 4 (PORT 2) connects directly through W100 to Pin 1 (PORT 1) where it is output to the antenna circuit. The connection between Pin 9 (PORT 3) and Pin 6 (PORT 4) is part of the sensing circuit (See Figure 4).

RF Output		RF Input
1	Port 1	Port 2
	GND	GND
	Port 3	Port 4
50 Ohms		Power Sense
		Circuit N102-A

Figure 6 - Directional Coupler

MMIC Buffer Amplifier

When transmitting, the collector voltage for transistor V104 is provided through PIN diode V101 and is controlled by DPTT. The RF output from the collector (+3 dBM) connects through coupling capacitor C116 and resistor R105 to power amplifier N101, Pin 1 (Pin/Vc).

SAW Transmit Band Pass Filter 2

The output of the MMIC Buffer amplifier is fed to the input of the second SAW BPF. This filter provides further attenuation for Tx spurions. The output of this filter is fed to the RF amplifier

Power Amplifier (N101)

Power amplifier N101 is a three stage Class C operated RF power amplifier module designed to operate over the frequency range of 896-940 MHz (see Figure 5).

1	2	3	4	5
Pin/Vc	Vdd1	Vdd2	Vdd3	Pout

Figure 5 - Power Amplifier

Power Sensor Circuit (N102-A)

The power sensor circuit consist of part of W100, comparator amplifier N102-A and associated circuitry in between. A regulated 5.5 volts (VTX) from transmit regulator N190 is applied to N102-A, Pin 8, (V+). This voltage forward biases Schottky diodes V103-1 and V103-2. When forward biased diode V103-1 has 0.3 volts on the anode, a reference voltage of 0.15 volts is on N102-A, Pin 3 (+IN). Forward biasing V103-2 causes a current to flow through directional coupler W100 (PORT 3 and PORT 4). This circuit provides temperature compensation for power detection. A voltage directly proportional to the RF power output is applied to N102-A, Pin 2 (-IN). This is due to the rectification of the coupled RF energy into V103-2. A negative DC voltage is developed at the anode of V103-2 proportional to the coupled RF power. This negative DC voltage results in a positive DC voltage at the output of N102-A. This output is the TX_PWR_SENSE line and can be metered at test point TP102. At 3 watts output this voltage is typically between 2.8 Vdc and 3.2 Vdc. This line connects to DEBBIE, Pin 52 (D601) through decoupling circuit resistors R602 and R603 and capacitor C601. DEBBIE converts this DC level to a digital word which is fed to the microprocessor in HILLARY. This word is compared to the value in Tracking Data which represents 3 watts of output power. A word is then generated and fed

back to DEBBIE. DEBBIE generates a TX_POWER_CONTROL DC signal on Pin 62 (DAC01). This signal connects through a decoupling circuit consisting of resistors R614 and R615 and capacitor C605 to a voltage