In a radio tuner or the like, by mixing a local signal separated by an intermediate frequency (IF) from a desired station frequency by a mixer with an RF signal for which an arriving radio wave is received by an antenna, the RF signal of a desired station is down-converted to an IF signal, and the obtained IF signal is filtered in an IF filter to take out a desired station signal.
Then, the IF filter is requested to appropriately take out the desired station signal. Thus, it is desired to accurately set a passing band of the IF filter, and a center frequency F0 of the IF filter is adjusted. Although a ceramic filter whose passing band is accurate is also used, it cannot be incorporated in an IC and is externally attached.
Conventionally, in F0 adjustment of the IF filter, an adjustment method utilizing a replica oscillation circuit is used. In the adjustment method, a replica circuit simulating an IF filter circuit in a tuner is oscillated and the oscillation frequency is counted by a frequency counter. Then, by adjusting the oscillation frequency of the replica oscillation circuit to be an F0 value and reflecting the adjustment result on the F0 adjustment of the IF filter, the IF filter is adjusted.
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