The method of 300MHz isolated handheld oscilloscope design

Abstract

Isolated handheld oscilloscope is an indispensable measuring tool in the measurement. It has the characteristics of portability, flexible utilization and high safety performance. Conventional handheld oscilloscopes isolate the analog channels through transformers or optocouplers, but the bandwidth of oscilloscopes is limited due to the bandwidth limitations of the transformers and the drifting characteristics of the optocouplers. This paper presents a new isolation scheme through digital channels. Because the digital isolation chips can transmit at large rate and perform multiple channels in parallel, the transmission rate can theoretically unlimited grow. The bandwidth of the oscilloscope is only related to the analog channel. By means of digital channel isolation, the bandwidth of the isolated oscilloscope is not affected by the isolation channel, and reaches the maximum bandwidth of the traditional non-isolated oscilloscope. At present, the isolated oscilloscope by analog channels on the market has bandwidth of 200 MHz.However,the bandwidth of the non-isolated oscilloscope has reached 500 MHz or even 1 GHz. Based on this scheme, a dual-channel isolated handheld oscilloscope is designed with single channel sampling rate 2GSa/s and 300MHz bandwidth. The isolation between oscilloscope channels security level can reach CAT II 1000V, CAT III 600V. Its bandwidth is larger than the handheld oscilloscope on the analog channel isolation in the markets.