HMC1023LP5E Datasheet, PDF (24/30 Pages) Hittite Microwave Corporation – Anti-aliasing and reconstruction filters

v01.0113
HMC1023LP5E
72 MHz DUAL PROGRAMMABLE
LOW PASS FILTER WITH DRIVER
Table 12. Calibration Code Look up Table
fine_bandwidth_code [3:0]
min
(MHz/MHz)
fine_tune_ratio
typ
(MHz/MHz)
max
(MHz/MHz)
0000
0.790
0.803
0.818
0001
0.818
0.832
0.846
0010
0.846
0.862
0.878
0011
0.878
0.893
0.909
0100
0.909
0.926
0.943
0101
0.943
0.959
0.976
0110
0.976
0.994
1.012
0111
1.012
1.030
1.048
1000
1.048
1.063
1.078
1001
1.078
1.097
1.116
1010
1.116
1.136
1.155
1011
1.155
1.183
1.210
To reprogram the HMC1023LP5E to any other bandwidth simply repeat the steps above.
Filter Bandwidth Setting After Calibration
In cases where ctune is unknown but the calibrated and programmed bandwidth is known, it is possible to estimate
the value of ctune based on the values of Coarse Bandwidth Code and Fine Bandwidth Code and the corresponding
values in Table 11 and Table 12.
For example, if the 3 dB bandwidth for the HMC1023LP5E was factory pre-programmed to a customer defined
requirement of 34 MHz and Reg 02h[9:6] = “0110” (Coarse Bandwidth Code) and Reg 03h[3:0] = “0010” (Fine
Bandwidth Code), as determined from Reg 0Ah for a pre-programmed part or from Reg 02h & Reg 03h for a non
programmed part, then ctune can be estimated as follows:
1. Lookup the nominal coarse bandwidth and fine bandwidth frequencies.
a. From Table 11 the nominal coarse frequency is 40 MHz
b. From Table 12 the nominal fine normalized frequency is 0.862 MHz/ MHz or simply 0.862
2. Estimate ctune as:

ctune=(40 MHz * 0.862 )/ 34 MHz = 1.0141
This value of ctune can now be used to calculate any arbitrary filter frequency as described above.
RC Calibration Circuit
The RC Calibration block uses a known user supplied clock to measure an on chip RC time constant. This measurement
is representative of the uncorrected corner frequency error for a given bandwidth for the HMC1023LP5E.
Calibration is normally done at room temperature. Refer to “Table 1. Electrical Specifications” for further details on the
variation of the 3 dB cutoff point with temperature. Typically programmed bandwidth varies 0.03 %/ºC.
With this information, the HMC1023LP5E can correctly fine tune the LPF by adjusting the resistors in the LPF to center
the corner frequency to the desired bandwidth.
To calibrate the HMC1023LP5E proceeds as follows:
1. Apply a clock signal of frequency between 20 MHz and 100 MHz on the CALCK pin (pin 11) of the
HMC1023LP5E. The clock signal only needs to be applied during the calibration procedure and is not
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