The Integrated Circuit Design Of RS232 Transceiver

RS-232 interface is one of Serial typical interface in computer. It Transmits data and control signal by one bit after another bit, it is suitable for long distance communication, it can debase the price of corresponding circuitry and predigest corresponding equipment. Based on the RS-232 communication protocol, an RS-232 tranceiver using ASMC 1μm CMOS high voltage technology is presented in this paper, the transceiver can achieve voltage conversion between TTL/CMOS and EIA/TIA RS-232.First, the chip's block diagram is introduced, it contains three parts: positive, negative double charge pump; two channel receivers; two channel transmitters. According to the RS-232 standards, the voltage doublet should supply DC voltages higher +8V and lower -8V to the transmitters, and exterior of the chip only links four 1μF eramic capacitors, so it can reduce disturbtion of EMI and the cost. In designing the receivers, hysteretic comparators to bring out 1.7V high threshold voltage and 1.1V low threshold voltage is used, so it makes the receivers have high Sensitivity and high ability of anti-jamming, its propagation delay is 0.43μs. The transmitters must output RS-232 voltage, it makes the output V₊ (8.83V) and V_-8.57V of charge pump as the power voltage, and outputs high voltage 8.61V and low voltage -8.47V, its propagation delay is 2.9μs. In the end, 15KV ESD protection using two diodes is designed, which NMOS linking gate to gnd and PMOS linking gate to Vcc.Based on the principle analysis and circuit design, the system and its sub-circuits are simulated by EDA tools Cadence Spectre, the simulation results reach the requests and verified the correctnesss of the principle analysis and circuit design.