A Multi-Functional 300 to 930 MHz RF transceiver IC. (Product Feature).
This article describes the fundamental architecture and explains some design applications of a fully integrated transceiver chip that is designed in a RF-dedicated 0.6mm BiGMOS process. The new TH7120 half-duplex transceiver IC is a single chip solution that requires only a few external components and is mounted in a LQFP32 surface-mount package. It features a phase-locked loop (PLL) stabilized RF voltage-controlled oscillator (VCO) with locked loop detection in a multi-channel mode and a 3wire bus serial control interface. The IC offers FSK/ASK modulation selection, FSK for digital data and FM for analog signal reception, a received signal strength indicator (RSSI) and ASK detection. In addition, there is switchable low noise amplifier (LNA) gain for improved dynamic range and an automatic PA turn-on after PLL lock. FM is possible with an external varactor and ASK modulation is achieved by on/off keying. An AFC option is available for extended input frequency acceptance range.
TECHNICAL SPECIFICATIONS AND CONFIGURATION
The main technical parameters of the TH7120 IC include an input frequency range of 300 to 950 MHz with an adjustable output power range from -15 to +6 dBm. The power supply range is from 2.5 to 5.5 V with an operating current of 6.0 mA in receive mode at low gain and 9.0 mA in transmit mode at nominal output power. Standby current is 50 nA.
The transceiver IC accepts a 3 to 12 MHz crystal reference. The maximum data rate is 60 kbps NRZ. Maximum input level is -10 dBm at FSK and -20 dBm at ASK. The input frequency acceptance is [+ or -]50 kHz (with AFC option). Input sensitivity is -103 dBm at ASK with 280 kHz IF filter BW and -105 dBm at ASK with 280 kHz IF filter BW. Frequency deviation range is [+ or -]5 kHz to [+ or -]100 kHz and the maximum analog modulation frequency is 20 kHz. The IC operates from -40[degrees] to +85[degrees]. The block diagram shown in Figure 1 depicts the transceiver's functional building blocks.
The receive path is mainly constituted by the LNA, downconversion mixer (MIX), intermediate-frequency amplifier (IFA) chain and FSK demodulator. A pair of operational amplifiers (OA1 and OA2) can be used to setup different data slicer configurations in FSK and ASK mode and to configure an automatic-frequency control (AFC) circuit.
Part of the transmitter chain is the VCO that is stabilized by the PLL synthesizer consisting of programmable N and R counters as well as a phase-frequency detector (PFD) with a charge pump and crystal reference oscillator (RO). The VCO output signal is amplified by the power amplifier (PA) to deliver the final transmitter carrier signal.
ASK modulation is performed via on/off keying of the PA, while FSK is generated by modulating the RO frequency through pulling of a crystal. The internal switch at pin FSK_SW can be employed to activate/deactivate an external pulling capacitor. The pin ASK/FSK is utilized to do the modulation type selection.
The TH7120 offers a maximum of flexibility. It can be configured either as a fixed-frequency stand-alone transceiver or as a multi-channel programmable device. The first setup allows the selection of one of the commonly used ISM/SRD band frequencies at 315, 433.92, 868.3 or 915 MHz. In this mode, hand selection is accomplished by setting pins FS0/SDEN and FS1/LD to logic HIGH or LOW. Running the transceiver in programmable mode means the internal PLL frequency synthesizer is controlled by an external controller. For this reason, programming can be accomplished via the serial 3wire bus interface at pins FS0/SDEN, TE/SDTA and RE/SCLK.
FIXED-FREQUENCY APPLICATION CIRCUITS
Figures 2 and 3 depict the application circuits to form a complete FSK or ASK transceiver system operating at any of the fixed frequencies, respectively.
One of the differences between the two very simple, and likewise popular, modulation schemes is that ASK is relatively robust against frequency tolerances of the TX carrier and RX local oscillator. FSK, on the other hand, requires higher frequency stability on both sides of the communication channel in order to function properly. Other issues, including large-signal handling capability or a better signal-to-noise ratio, for example, are advantages of the FSK format. If the system designer is in favor of FSK, for whatever reason, an AFC feature in the receiver is a welcome plus. The TH7120 receive path meets this requirement by adding an external varactor diode that tunes the FM (FSK) demodulator tank, as shown in Figure 4.
PROGRAMMABLE MULTI-CHANNEL APPLICATION CIRCUITS
An industry-standard 3wire bus serial interface is part of the TH7120 IC. It can he utilized in case the user needs to run a multi-channel and frequency-agile wireless link. The programming can be done via a microcontroller or any other appropriate digital circuit. The company offers an evaluation software package that helps check out the TH7120 transceiver's programmability. It can be operated via a PC'S printer port.
The aim of this article has been to provide insight into the versatility of the new TH7120 transceiver IC. It has been shown how the user can setup a transceiver system perfectly matched to his or her needs. The TH7120 bridges the gap between the company's existing line of transmitter (TH7107 to TH71082) and receiver (TH7110 to TH71112) circuits.
Samples of the TH7120 are currently available. Full demo kits consisting of an evaluation board and the 3wire bus control software are also available.
Circle No. 301
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|Comment:||A Multi-Functional 300 to 930 MHz RF transceiver IC. (Product Feature).|
|Article Type:||Brief Article|
|Date:||Nov 1, 2001|
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