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Method for high-speed frequency-to-voltage conversion with a minimum of ripple on the output signal over a wide input-frequency range

IP.com Disclosure Number: IPCOM000009891D
Publication Date: 2002-Sep-25
Document File: 5 page(s) / 119K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method for high-speed frequency-to-voltage (F/V) conversion with a minimum of ripple on the output signal over a wide input-frequency range. Benefits include improved functionality and improved performance.

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Method for high-speed frequency-to-voltage conversion with a minimum of ripple on the output signal over a wide input-frequency range

Disclosed is a method for high-speed frequency-to-voltage (F/V) conversion with a minimum of ripple on the output signal over a wide input-frequency range. Benefits include improved functionality and improved performance.

Background

� � � � � The two best-known and most-used conventional approaches for F/V converters are analog and digital.

Analog

        � � � � � An F/V converter with an analogue voltage output is a conventional solution (see Figure 1). The duty cycle on the input signal may be fixed at 50% (50% high, 50% low). Because the monostable multivibrator (MMV) generates one pulse with a fixed width for each positive edge on the input (Fin), the duty cycle out of the MMV varies with the frequency on the input. Filtering (heavily) on this signal from the MMV results in a reprehensive voltage on the output.

        � � � � � In a typical design, the pulse width of the MMV is equal to the period time of the maximum frequency to be converted. The RC time is set to a constant frequency so that the lowest frequency to be converted is as ripple free at output as the application requires.

        � � � � � If a wide frequency range is required, a tradeoff must occur between the frequency range and the response time because the RC time constant is set for the lowest frequency. The amount of output signal ripple is proportional to the frequency of the input, so the high frequencies are precise (ripple free). The low frequencies are imprecise (heavy ripple).

        � � � � � With this approach, the response time for getting the high frequencies converted are extremely large in comparison to the outcome when the RC is set for filtering only one (high) frequency.

Digital

        � � � � � An F/V converter with a digital voltage output is a conventional solution (see Figure 2). The oscillator labeled OSC1 determines the lowest frequency to be converted. The size/depth of counter labeled C1 determines the highest frequency.

        � � � � � If a wid...