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Interfacing circuit of Demodulator with AGC receiver RF2667 chip and its application

Published on Oct 29 2010 // Micrcontroller circuits


Interfacing circuit of Demodulator with AGC receiver RF2667 chip and its application 2

Interfacing circuit of Demodulator with AGC receiver RF2667 chip and its application

Abstract: RF2667 RF Micro Device is produced with the receiver AGC in CDMA / FM demodulator chip. The chip integrates a complete IF automatic gain control (AGC) amplifier and quadrature demodulator, can be used in dual-mode CDMA / FM cellular mobile communication systems and PCS systems. This paper introduces the RF2667 principle, characteristics and typical application circuit.
1 Overview
RF Micro Device’s chips in its complete integrated RF2667 IF automatic gain control (AGC) amplifier and quadrature demodulator. This makes the RF2667 can be used for dual-mode CDMA / FM cellular mobile communication systems and PCS systems. The chip in the receiver IF signal amplification, it can provide 100dB of gain control range, and the IF signal demodulation for the I and Q channel signals. The chip’s key indicators (such as noise figure and IP3, etc.) and CDMA cellular mobile communication system standard IS-98 and J-STD-018 compliant. It uses advanced silicon bipolar process (FT = 15GHz) for manufacturing. While a standard 24-pin SSOP package small. RF2667 The main features are as follows:
* And RF9957 similar, but higher than the RF9957 I / O output voltage;
* Support for dual-mode (CDMA and FM);
* Low power mode with a digital control;
* Power is 2.7 ~ 3.3V;
* Power is 2.7 ~ 3.3V;
* With the quadrature LO divider;
* IF AGC amplifier with internal gain control range of 100dB.
RF2667 demodulator chip for its excellent properties can be widely used in CDMA / FM cellular communication systems, CDMA PCS systems, GSM / DCS systems, TDMA systems, spread spectrum cordless phones, wireless local loop systems, and general purpose digital high-speed data Modem receivers and other systems.

2 internal structure
RF2667 includes input selection circuit, the gain control circuit, reference signal demodulation circuit and time slots, in which the input selection circuit is used for CDMA or FM input signal input signal selection. The role of automatic gain control circuit is a device to receive the CDMA or FM signal demodulator AGC amplification to enable them to better demodulation processing. AGC received signal amplification is RF2667 feature of the chip. Figure 1 shows the internal block diagram RF2667.
3 pin function and application circuit
Figure 2 shows the typical application circuit RF2667. The figure also shows the pinouts RF2667, now its the power of this pin as follows:
1 foot (VCC1): The oscillator triggers, crossover and limiting amplifier power side. The side with the pin 2 and 3 in parallel. And should be connected 0.01µF bypass circuit. In the PCB, the pin and the bypass capacitor should be as short as possible connections between, and the bypass capacitor ground terminal should be connected directly to ground plane.
Pin 2 (VCC2): band gap voltage source, gain control bias circuit and the AGC of 2,3,4-level power supply terminal.
3 pin (VCC3): FM and CDMA in the AGC input stage of the supply side.
4,5 feet (CDMA IN +, CDMA IN-): CDMA balanced input. The end of the internal plus a DC bias. In the single-ended input application, which the foot is used as input, the other end of AC-coupled to ground. Balanced input impedance input 2.4kO, single-ended input mode input impedance of 1.2kO.
6,7,17,20 pin (GND): ground. For best performance, the connection between the endpoint and the earth should be as short as possible.
8,9 feet (FM IN +, FM IN-): FM balanced input. The side also included a DC bias within. In the single-ended input application, which the foot is used as input, the other end of AC-coupled to ground. The balanced input pin in the input impedance of 2.4kO, single-ended input mode input impedance of 1.2kO.
10 feet (BGOUT): band gap voltage reference. This voltage in the entire temperature range and power range remain unchanged, providing bias for the internal circuitry. Should be an external 0.01µF bypass capacitor. This pin and the bypass capacitor should be as short as possible connections between, and the bypass capacitor ground terminal should be connected directly to ground plane.
11 feet (DEC): AGC decoupling end. The feet also need to connect an external 0.01µF bypass capacitor. And this pin and the bypass capacitor connected between should try shorter, while the land-side bypass capacitor should be connected directly to the ground.

Figure 2 RF2667 CDMA system in a typical application circuit Click to enlarge
12,13 feet (LO-, LO +): LO balanced input. The end of the content plus a DC bias. In the single-ended input application, which the foot is used as input, the other end of AC-coupled to ground. As the signal frequency 12,13 feet internally divided by 2, so the modulator carrier frequency is half the applied frequency. This balanced input ends of the input impedance of 800O, single-ended input mode input impedance of 400O. Although the LO side can work with single-ended input mode, it can be balanced input, but can better balance the input and the corresponding gain the best balance.
14 feet (INSEL): CDMA and FM mode selection input for data input. The end of logic high, the selected CDMA mode, the client logic low, the selected FM mode. The foot resistance is 30kO.
15,16 feet (QOUT-, QOUT +): Q baseband output balanced mixer. Since the end of the internal plus a DC bias Villa, which requires use of additional external blocking capacitors. This output in the CDMA mode and FM mode, are active. However, single-ended configuration, the two outputs in an unused, so the output voltage will be reduced by half. The single-ended output port impedance is 1.2kO, balanced output impedance is 2.4kO.
18,19 feet (FL-, FL +): balanced output AGC / demodulator input.
21,22 feet (IOUT +, IOUT-): I balanced mixer baseband output. The plus side there is the internal dc bias, need to use additional external blocking capacitors. This output in the CDMA mode and FM mode, are active. In the single-ended configuration, the two outputs in an unused, the output voltage will be reduced by half. Single-ended output impedance is 1.2kO, balanced output impedance is 2.4kO.
23 feet (GC): AGC amplifier analog gain control. Control voltage range of 0.5 ~ 2.5VDC. AGC gain range is 95dB.
24 feet (PD): low-power control. This terminal is logic 1, all the circuit work; this terminal is logic 0, all the circuitry is shut down.