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HMC703LP4E

v02.0813

8 GHz fractional syntHesizer

For price, delivery and to place orders: Hittite Microwave Corporation, 2 Elizabeth Drive, Chelmsford, MA 01824

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PD Polarity

Reg 0Bh[4]=0 sets the PD polarity for use with a passive loop filter together with a VCO with a positive tuning slope

(increasing tuning voltage increases VCO frequency).

Reg 0Bh[4]=1 inverts the PD polarity. This is most often used if an inverting op-amp is used in an active loop filter

together with a VCO with a positive tuning slope.

charge Pump tri-state

Reg 0Bh[5]=Reg 0Bh[6]=0 tri-states the charge pump. This effectively freezes charge on the loop filter and allows the

VCO to run open loop, provided that CP offset is also disabled.

charge Pump Gain

Reg 09h[6:0] and Reg 09h[13:7] program current gain settings for the charge pump. Pump ranges can be set from 0 µA

to 2.54 mA in 20uA steps. Charge pump gain affects the loop bandwidth. The product of VCO gain (Kvco) and charge

pump gain (Kcp) can be held constant for VCO’s that have a wide ranging Kvco by adjusting the charge pump gain. This

compensation helps to keep the loop bandwidth constant.

In addition to the normal CP current as described above, there is also an extra output source of current that offers

improved noise performance. HiKcp provides an output current that is proportional to the loop filter voltage. This being

the case, HiKcp should only be operated with active op-amp loop filters that define the voltage as seen by the charge

pump pin. With 2.5 V as observed at the charge pump pin, the HiKcp current is 3.5 mA.

There are several configurations that could be used with the HiKcp feature. For lowest noise, HiKcp could be used

without the normal charge pump current (the charge pump current would be set to 0). In this case, the loop filter would

be designed with 3.5 mA as the effective charge pump current.

Another possible configuration is to operate with both the HiKcp and normal charge pump current sources. In this case

the effective charge pump current would be 3.5mA + programmed normal charge pump current which could offer a

maximum of 6 mA.

With passive loop filters the voltage seen by the charge pump pin will vary which would cause the HiKcp current to vary

widely. As such, HiKcp should not be used on passive loop filter implementations.

A simplified diagram of the charge pump is shown in Figure 39. The current gain of the pump in Amps/radian is equal

to the gain setting of this register divided by 2π.

charge Pump offset

Reg 09h[20:14] controls the charge pump current offsets. Reg 09h[21] and Reg 09h[22] enable the UP and DN offset

currents respectively. Normally, only one is used at a time. As mentioned earlier charge pump offsets affect fractional

mode linearity . Offset polarity should be chosen such that the divided VCO lags the reference signal. This means

down for non-inverting loop filters.

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responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other

rights of third parties that may result from its use. Specifications subject to change without notice. No

license is granted by implication or otherwise under any patent or patent rights of Analog Devices.

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HMC703LP4E Datasheet(PDF) 35 Page - Analog Devices

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