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1940年,William Hewlett和DavidPackard两人将他们在车库中制作的一种产品投放市场,这种产品就是维氏电桥(Wien-Bridge)振荡器。它由一个单极点高通滤波器与一个单极点低通滤波串联而成。为了保持增益恒定不变,该振荡器电路采用一只白炽灯作指示灯来提供AGC(自动增益控制)。正如所有的白炽灯那样,这种指示灯具有非线性的电阻值。当你给这一振荡器电路通电时,冷白炽灯的电阻很小,从而产生很高的增益。随着增益的增大,温度不断升高的白炽灯的电阻也随之增大。因此,白炽灯具有AGC功能。这种振荡器电路一直使用了60多年,现在仍然在使用中。维氏电桥振荡器存在的唯一问题就是,增益小于1时,它不工作。我在一家电话公司供职时,
In 1940, William Hewlett and David Packard put on the market a product they made in the garage, the Wien-Bridge oscillator. It consists of a single-pole high-pass filter and a single-pole low-pass filter connected in series. In order to keep the gain constant, the oscillator circuit uses an incandescent lamp as an indicator to provide AGC (Automatic Gain Control). As with all incandescent lamps, this indicator has a non-linear resistance value. When you power on this oscillator circuit, the cold incandescent lamp has a small resistance and therefore a high gain. As the gain increases, the temperature of the incandescent lamp is also increasing the resistance. As a result, incandescent lamps have the AGC function. This oscillator circuit has been in use for more than 60 years and is still in use. The only problem with a Vickers bridge oscillator is that it does not work when the gain is less than one. When I worked for a phone company,